Firstly: Intellect
1. Trade with a mentally unwell person is not valid:
Evidences:
(1) From the Sunnah
`A’ishah narrated that the Messenger of Allah said, “The pen has been lifted from three: From the sleeping person until they wake up, from the young person until they grow up, and from the mentally unwell person until they regain their intellect or come to their senses.” [63] Reported by Nasa’i (3432), Ibn Majah (2041), and Ahmad (24694). The wording here is from Nasa’i. Bukhari said, as found in Al-`Ilal al-Kabir by Tirmidhi (225): “I hope that it is preserved.” Graded sahih by Hakim, who said, “Upon the conditions of Muslim”, and by Ibn al-`Arabi in `Aridat al-Ahwadhi (3/392). Ibn Kathir said in Irshad al-Faqih (1/89): “Its chain is upon the conditions of Muslim.” Ibn Hajar said in Fath al-Bari (12/124): “It has a supporting proof and it has paths of transmission that strengthen each other.” Graded sahih by Albani in Sahih Sunan al-Nasa’i (3432), and Shu`ayb al-Arna’ut graded its chain jayyid in his explication of Musnad Ahmad (24694). This hadith has a supporting evidence in the narration of `Ali h.   Reported by Tirmidhi (1423) with the wording “the mentally deranged until they regain their intellect”; Ahmad (956); and Nasa’i in Al-Sunan al-Kubra (7346) with some doubt [regarding the wording], “the mentally deranged or the drunk person until they regain their intellect.” Graded hasan by Bukhari, as found in Al-`Ilal al-Kabir by Tirmidhi (226). Ahmad Shakir graded its chain sahih in Tahqiq al-Musnad (2/197). Albani graded the narration sahih in Sahih Sunan al-Tirmidhi (1423), and Shu`ayb al-Arna’ut graded it sahih by way of supporting evidences in his explication of Musnad Ahmad (1183).

(2) From the scholarly consensus
A scholarly consensus on this issue was related by Mawardi, [64] Mawardi said: “As for the mentally unwell person, by scholarly consensus, his purchase is invalid and does not depend on the permission of the guardian.” Al-Hawi al-Kabir (5/368). Ibn Hazm, [65] Ibn Hazm said: “The scholars agreed that the sale of a person whose intellect is affected by something other than an intoxicant is invalid, and the same goes for his purchase.” Maratib al-Ijma`, p. 84. Ibn al-`Arabi, [66] Ibn al-`Arabi said: “As for the prerequisite of the intellect, it is because the statement of a mentally unwell person, by the consensus of the scholars, holds neither sense nor legal weight.” Al-Qabas fi Sharh Muwatta’ Malik ibn Anas, p. 776. Ibn al-Qattan, [67] Ibn al-Qattan said: “The scholars agreed that the sale of a person whose intellect is afflicted by something other than an intoxicant is invalid, and the same goes for his purchase.” Al-Iqna` (2/211). Nawawi, [68] Nawawi said: “As for the mentally unwell person, his sale is invalid by scholarly consensus, and the same goes for an unconscious person.” Al-Majmu` (9/155). and Ibn Taymiyyah. [69] Ibn Taymiyyah said: “As for the mentally unwell person from whom the pen has been lifted, by the consensus of the scholars, none of their acts of worship are valid. Neither faith, disbelief, prayer, nor any other act of worship are valid on their part. Furthermore, according to most rational people, they are not suited to worldly affairs such as trade or industry. It is not suitable for such a person to be a fabric merchant, perfume seller, blacksmith, or carpenter, and their contracts are invalid according to the consensus of the scholars. Therefore, their sale and purchase are [also] invalid.” Majmu` al-Fatawa (11/192).

(3) Because dealing with wealth, just like looking after wealth, is not entrusted to mentally unstable individuals. [70] Al-Majmu` by Nawawi (9/156).
Trade with a drunk person
Trade with a person who has a legitimate excuse for their drunkenness
Trade with a person who has a legitimate excuse for their drunkenness [71] For example, a person who drinks an intoxicant unknowingly, or a person who is forced to drink an intoxicant against their wishes. is not valid, and this is agreed upon by the four jurisprudential schools of thought: the Hanafis, [72] Hashiyat Ibn `Abidin (3/239, 240), Al-Fatawa al-Hindiyyah (5/415). Malikis, [73] According to the Malikis, trade with a drunk person is invalid in all circumstances. Mawahib al-Jalil by Hattab (5/308) and Hashiyat al-Dasuqi ?ala al-Sharh al-Kabir (2/366). Shafi`is, [74] Mughni al-Muhtaj by Shirbini (2/219) and Nihayat al-Muhtaj by Ramli (5/55). and Hanbalis. [75] According to the Hanbalis, trade with a drunk person is invalid in all circumstances. Al-Mubdi` by Burhan al-Din Ibn Muflih (3/346) and Kashshaf al-Qina` by Bahuti (3/151). This is because a drunk person is like a mentally unstable person. [76] Hashiyat al-Dasuqi ?ala al-Sharh al-Kabir (2/366) and Mughni al-Muhtaj by Shirbini (2/219).

Trade with a person who consumes an intoxicant by their own volition:
Trade with a person who consumes an intoxicant by their own volition is not valid, and this is the school of thought of the Malikis, [77] Mawahib al-Jalil by Hattab (6/31, 32) and Hashiyat al-Dasuqi ?ala al-Sharh al-Kabir (2/366; 3/397). Hanbalis, [78] Al-Mubdi` by Burhan al-Din Ibn Muflih (3/346), Kashshaf al-Qina` by Bahuti (3/151), and Matalib ‘Uli al-Nuha by al-Rahibani (3/10). and one of the positions of the Shafi`is; [79] Al-Majmu` by Nawawi (9/155). the view of Ibn Hazm; [80] Ibn Hazm said: “It is neither permissible to sell to a person who has lost their mental capacity due to intoxication or mental illness, nor to compel them [to do so].” Al-Muhalla bi al-Athar (7/507). and the preferred opinion of Ibn Taymiyyah, [81] Ibn Taymiyyah said: “Their acts of worship (i.e., intoxicated people) are like their prayer: invalid according to textual evidence and scholarly consensus. Allah prohibited approaching the prayer whilst intoxicated until they are cognizant of what they are saying, and the people agreed upon this…and it is well known that their prayer is invalid, for they do not know what they are saying, as is indicated in the Qur’an. We say: whoever’s acts of worship are invalid due to their lack of mental capacity, then it is even more befitting and appropriate for their contracts to be [considered] invalid, like a person who is asleep, a mentally unwell person, and so on.” Al-Fatawa al-Kubra (4/204). He also said: “The scholars disagreed regarding the contracts of an intoxicated person, such as a divorce, and their unlawful actions, such as murder or fornication; are they considered in the same way as the actions of a sane person or the actions of a mentally unstable person, or is there a distinction between their statements and actions, or between some actions and statements and others? There were several well-known positions regarding this matter. That which is indicated by the texts, the fundamental principles, and the statements of the Companions is that their statements are considered invalid, like [those of] a mentally unstable person, and that they neither enact a divorce nor any other [contract or agreement].” Majmu` al-Fatawa (14/115). Ibn al-Qayyim, [82] Ibn al-Qayyim said: “The correct opinion is that their statements (i.e., intoxicated people) hold no weight in terms of divorce, manumission [of slaves], sale, gifting, endowment, [embracing] Islam, apostasy, or testimony.” `Ilam al-Muqi`in (5/454). and Ibn `Uthaymin. [83] Ibn `Uthaymin said: “The stronger opinion regarding intoxicated people is that all their statements, including both their contracts and their depravity, are meaningless. All their statements are meaningless, for if an intoxicated person was to say, ‘My wives are hereby divorced, my slaves are hereby freed, and my properties are hereby [gifted as] endowments’, none of that would be implemented, because he is lacking in mental capacity and is not cognizant of what he is saying. As Allah Exalted says: ‘O believers! Do not approach prayer while intoxicated until you are aware of what you say’ (al-Nisa’, 43).” Fath Dhi al-Jalal wa al-Ikram bi Sharh Bulugh al-Maram (5/409).

Evidences:
(1) From the Book:
The Statement of Allah Exalted, “Do not approach prayer while intoxicated until you are aware of what you say.” [84] al-Nisa’, 43.
Allah clarifies in this verse that intoxicated people do not know what they are saying, therefore rulings cannot be made based on their statements until they are cognizant of what they are saying, for they are not being addressed in the command to prayer. [85] Al-Muhalla bi al-Athar by Ibn Hazm (7/507).

(2) From the Sunnah:
The statement of the Prophet, “Certainly, actions are judged according to intentions, and every person will have what they intended.” [86] Reported by Bukhari (1) and Muslim (1907) from `Umar h. The wording here is from Bukhari.

This means that every word that is uttered without an intention on the part of the speaker or is uttered by a person lacking their intellect cannot be used as a basis for rulings. [87] Majmu` al-Fatawa by Ibn Taymiyyah (33/107).

(3) Because an intoxicated person loses their intellect and therefore resembles a mentally unstable person, a person who is asleep, a person who lose their mental capacity through medicinal drugs and the likes. [88] Al-Mughni by Ibn Qudamah (4/279) and `Ilam al-Muqi`in by Ibn al-Qayyim (5/454).

(4) Because an intoxicated person lacks willpower and therefore resemble an individual who has been forced to do something. [89] Al-Mughni by Ibn Qudamah (4/279).

(5) Because a trade is a statement that is valued when uttered with consent, and therefore is only valid from a right-minded individual, as is the case with testimony. [90] Kashshaf al-Qina` by Bahuti (3/151).

(6) Because all statements and contracts are conditioned on the presence of discernment and reason. Therefore, the speech of a person who lacks discernment and reason is fundamentally devoid of any legislative significance. [91] Al-Mughni by Ibn Qudamah (4/206) and Majmu` al-Fatawa by Ibn Taymiyyah (33/107).

(7) Because intellect is a prerequisite of legal responsibility. It is an expression of command and prohibition, and that does not apply to someone who does not understand it. There is no distinction between whether the condition is lacking due to a disobedient act or other than that, based on the proof that if a person breaks their legs, then they are permitted to pray sitting down, if a pregnant woman strikes her stomach and miscarries, then the obligation of prayer is lifted from her, and if a person strikes their head and loses their sanity as a result, then their legal responsibility is dropped. [92] Al-Mughni by Ibn Qudamah (4/206).

(8) Because their acts of worship (i.e., intoxicated people) are like their prayer, invalid according to textual evidence and scholarly consensus, and whoever’s acts of worship are invalid due to their lack of mental capacity, then it is even more befitting and appropriate for their contracts to be considered invalid. [93] Majmu` al-Fatawa by Ibn Taymiyyah (33/107).

Secondly: Puberty
1. The trade of a youth below the age of distinction when the item is significant
The trade of a youth below the age of distinction when the item is significant is not valid. This is agreed upon by the four jurisprudential schools of thought: [94] The majority – the Hanafis, Malikis, and Shafi`is – did not distinguish between children trading in small or significant items, but the Hanbalis did, allowing them to trade when the item is small. the Hanafis, [95] Tabyin al-Haqa’iq by Zayla`i (5/219) Al-Bahr al-Ra’iq by Ibn Nujaym (8/121). the Malikis, [96] Mawahib al-Jalil by Hattab (6/31) and Minah al-Jalil by `Ulaysh (4/437, 441). the Shafi`is, [97] Tuhfat al-Muhtaj by Ibn Hajar al-Haytami (4/227), Mughni al-Muhtaj by Shirbini (2/7). See also Al-Ghurar al-Bahiyyah by Zakariyya al-Ansari (2/396). and the Hanbalis, [98] The Hanbalis made an exception for small items, which they considered valid for youths below the age of distinction to trade in. Al-Mubdi` by Burhan al-Din Ibn Muflih (3/346), Al-Insaf by al-Mardawi (4/193), and Kashshaf al-Qina` by Bahuti (3/151). See also Al-Mughni by Ibn Qudamah (4/186). and that is because a condition of trade is consent and therefore it is a prerequisite for the person conducting the transaction to be permitted to act independently, as is the case with testimony. [99] Al-Mubdi` by Burhan al-Din Ibn Muflih (3/346).

2. The trade of a youth who has reached the age of distinction when the item is significant
The trade of a youth who has reached the age of distinction when the item is significant is valid if their guardian consents. If their guardian does not consent, however, then their trade is not valid. This was the school of thought of the majority: the Hanafis, [100] Tabyin al-Haqa’iq by Zayla`i (5/219), Al-Bahr al-Ra’iq by Ibn Nujaym (8/121), and Hashiyat Ibn `Abidin (5/107). the Malikis, [101] Mawahib al-Jalil by Hattab (6/31), Hashiyat al-Dasuqi ?ala al-Sharh al-Kabir (3/294), and Minah al- Jalil by `Ulaysh (4/437, 441). and the Hanbalis. [102] Al-Mubdi` by Burhan al-Din Ibn Muflih (3/346) and Kashshaf al-Qina` by Bahuti (3/151).

Evidences:
Firstly: From the Book
The Statement of Allah Exalted, “Test the competence of the orphans.” [103] al-Nisa’, 6.

Allah Exalted instructs testing orphans, which means to evaluate their competence, and this is done by empowering them to engage in buying and selling by permitting them to trade. [104] Kashshaf al-Qina` by Bahuti (3/151).

Secondly: Because such a youth is rational, capable of distinction, and legally competent, and it is valid for him to act with the permission of his guardian, as is the case with a slave. The difference between him and a youth who has not reached the age of distinction is that the latter will gain any advantage through his dealings because he is lacking in knowledge and discernment, and there is no need to test that because his nature in this regard is already well-known. [105] Al-Mughni by Ibn Qudamah (4/185).

3. The trade of a youth who has or has not reached the age of distinction when the item is small [106] Small items such as such as bread, a piece of candy, or other similar things that people commonly recognise as small. Matalib ‘Uli al-Nuha by Rahibani (3/10).

The trade of a youth who has or has not reached the age of distinction when the item is small is allowed, even without the permission of their guardian. This is the position of the Hanbalis, [107] Kashshaf al-Qina` by Bahuti (3/151) and Matalib ‘Uli al-Nuha by Rahibani (3/10). the view of Ishaq ibn Rahawayh, [108] Ibn al-Mundhir said: “Abu Thawr used to say: ‘Trade is not permissible for a child.’ It was reported that al-Kufi said: ‘His trade is permissible with the permission of his guardian and the authorisation of the judge.’ Sufyan al-Thawri said: ‘His trade is not permissible except with the consent of his family.’ Ahmad and Ishaq said the same, except for a small item, for they permitted the trade of small items but prohibited the trade of significant ones.” Al-Ishraf `ala Madhahib al-`Ulama (6/130) and Al-Awsat (10/358) by Ibn al-Mundhir. and the preferred view of Ibn `Uthaymin. [109] Ibn `Uthaymin said: “The apparent meaning of the author’s words is that the guardian’s permission for the mentally incapable person applies to both general and specific transactions. ‘General’ is when he says: ‘Take this money and trade with it.’ And ‘specified’ is when he says: ‘Take this money and trade with it in a specific thing, like chickens, eggs, or small items.’ This is the apparent meaning of the author’s words, but this apparent meaning is not intended. Rather, it is said: without the permission of his guardian in the specific thing, the person should come to him and say, ‘I want to buy (for example) a bird,’ and the guardian says, ‘Buy it.’ Or, he comes to him and says, ‘I want to sell my bird (for example)’, and he says, ‘Sell it’, except for small items that are customarily given to children, for there is no harm in that.   However, is it permissible to allow a mentally incapable person or a child [to trade] in order to please them and without considering the financial benefit? The answer is no, and for that reason we say, it is prohibited for the guardian to permit [them to trade] without any benefit.” Al-Sharh al-Mumti` (8/112).

Thirdly: The trade of a person who is considered legally incompetent due to their stunted understanding [110] “Safah”, or “limited understanding”, is a wastefulness of money and lack of prudence in handling it, which leads to its squandering in contradiction to the intrinsic principles of reason and the Shariah. Al-`Inayah by al-Babarti (9/259) and Hashiyat al-Dasuqi ?ala al-Sharh al-Kabir (3/292).

The trade of a person who is considered legally incompetent due to their limited understanding is not valid, and this is agreed upon by the four jurisprudential schools of thought: the Hanafis, [111] This is the relied-upon opinion, and it is the basis for the Hanafi legal verdict, contrary to the view of Abu Hanifa. It is deemed valid with the permission of his guardian or the judge. Al-Bahr al-Ra’iq by Ibn Nujaym (6/75) and Hashiyat Ibn `Abidin (5/110; 6/148). Malikis, [112] It is valid according to them with the permission of his guardian. Al-Taj wa al-Iklil by al-Mawwaq (5/58, 66), Mawahib al-Jalil by Hattab (6/35), Minah al-Jalil by `Ulaysh (6/89). Shafi`is, [113] Minhaj al-Talibin by Nawawi, p. 124; Tuhfat al-Muhtaj by Ibn Hajar al-Haytami (5/173); and Mughni al-Muhtaj by Shirbini (2/171, 172). and Hanbalis. [114] It is valid according to them with the permission of his guardian. Al-Mubdi` by Burhan al-Din Ibn Muflih (4/211) and Kashshaf al-Qina` by Bahuti (3/442).

(1) Because if his dealings were implemented, his wealth would be decimated, and there would have been no benefit in restricting his access to his wealth in the first place. [115] Al-Mughni by Ibn Qudamah (4/345).
(2) Because if his dealings were of benefit, his wealth would have been given to him, just as with a sane person. [116] Al-Mughni by Ibn Qudamah (4/345).
(3) Because declaring their transactions valid would entail nullifying the meaning of “restricted legal competence.” [117] Nihayat al-Muhtaj by Ramli (4/366).

Fourthly: Choice (i.e., consent)
1. The trade of a person who has been forced