The innate nature of human beings is to accept the existence of Allah, Exalted be He.
Allah, Most High, said, "And remember when your Lord brought forth from the loins of the children of Adam their descendants and made them testify as to themselves. Allah asked, “Am I not your Lord?” They replied, “Yes! We testify that You are our Lord.” (Quran 7:172) In this Statement, Allah, Exalted be He, addressed the Prophet (صلى الله عليه وسلم) by saying, "O Muhammad, recall when I summoned the progeny of Adam, bringing out the children of each one from their respective fathers and taking out all of them from the backbone of Adam, so I would take the covenant from them to acknowledge My Oneness. Allah, Exalted be He, asked them, “Am I not the Creator of all of you and the One whom you worship? They replied, Yes, we acknowledge and testify that you are."  [14] At-Tafseer al-Muharrar, Surah al-A’raaf, p 681.
Ibn ‘Abbaas (may Allah be pleased with them) narrated on the authority of the Prophet (صلى الله عليه وسلم) that he said, “Allah, Blessed and Exalted be He, took the covenant at Na‘maan (i.e., ‘Arafah), from the loins of Adam. He extracted from his loins every soul that Allah has predestined to be created, and He spread them before Himself like ants [15] That is, they were small in size like ants, Mirqaat al-Mafaateeh Sharh Mishkaat al-Masaabeeh by al-Qaari, 1/196. , then He spoke to them directly (what means): And mention when your Lord took from the children of Adam—from their loins—their descendants and made them testify of themselves, saying to them, "Am I not your Lord?" They said, "Yes, we have testified." This lest you should say on the day of Resurrection, "Indeed, we were of this unaware. Or lest you say, "It was only that our fathers associated others in worship with Allah before, and we were but descendants after them. Then would You destroy us for what the falsifiers have done? Quran 7:172-173” [16] Transmitted by Ahmad (2455), Ibn ‘Aasim in as-Sunnah (202), al-Firyaabi in al-Qadar (59), and an-Nasaai in as-Sunan al-Kubra (11127).
Aboo Hurayrah (may Allah be pleased with him) narrated, “The Messenger of Allah (صلى الله عليه وسلم) said, “Each child is born upon a sound innate nature. However, his parents make him a Jew or a Christian or a Magian.” Aboo Hurayrah then recited, "(This religion is) the original disposition from Allah upon which He originated (Literally: constituted) mankind. There is no altering (the laws of) Allah's creation. That is the most upright religion." (Quran 30:30)  [17] Transmitted by al-Bukhaaree (4775) and Muslim (2648).
Ibn Abee al-‘Izz said, “Undoubtedly, affirming the Lordship of Allah is a part of man’s innate nature. As for polytheism, it occurs at a later stage, which children take from their fathers. That is said, when they argue on the Day of Judgement that their fathers were polytheists and they only followed their way just like how it is the custom of people to follow the customs of their fathers in food, clothing, and accommodation,” they will be told, “You have already testified and acknowledged the Creator, and affirmed that Allah is Your Lord, and He has no partner.” [18] Sharh at-Tahhaawiyyah, 1/314.
Allah’s Existence is an intellectual necessity that makes it impossible for any person with a sound reason and sane mind to deny.
Allah, the Exalted, said, "Were they created by nothing, or were they themselves the creators?" (at-Toor: 35)
Ibn Taymiyyah said, “It is indeed known by intellectual necessity that there must be a Being who is eternal, and completely self–sufficient and independent of anything else. We observe that which is created brought into existence, such as animals, plants, and metals, and we know that which comes to existence is a possible existent; thus, it is neither impossible to exist nor necessarily existent. It is known of necessity that anything that comes to existence must have a Creator, and the possible existents do not come to existence on their own independently. This is as Allah, the Most High, said, “Were they created by nothing, or were they themselves the creators?” (at-Toor: 35) Knowing that they were not created by nothing, and that they did not create themselves, it is therefore becoming evident that they have a Creator who has created them. [19] At-Tadmuriyyah, p 20.
The fact that the Creator and the creation both exist does not mean that the form of their existence is the same.
The existence of the Creator is different from that of the creation, the existence of each of which is unique and befitting to their nature. For example, Allah’s existence is not preceded by non-existence, nor is it followed by demise – which is not the case when it comes to the creation that came into existence after they were non-existent. Allah, the Exalted, said, “He is the First (nothing is before Him) and the Last (nothing is after Him), the Most-High, (nothing is above Him) and the Most Near (nothing is nearer than Him). And He is the All-Knower of every thin.” (Al-Hadeed: 3)
Aboo Hurayrah (may Allah be pleased with him) narrated that the Prophet (صلى الله عليه وسلم) said in his supplication, “O Allah You are the First and nothing has come before you, and You are the Last, and nothing may come after You. You are the Most-High, nothing is above You and You are the Most Near, and nothing is nearer than You.” [20] Saheeh Muslim (2713).
Concerning the attributes of existence and life, Ibn al-Wazeer said, “The attributes of life and existence are used with reference to Allah to designate perfection that is free of any form of imperfection or deficiency. However, when they are used with reference to His slaves, they are intended to designate that they are subject to demise, death, sickness, calamities, and ailments.” [21] Eethaar al-Haqq ‘ala al-Khalq, p 277.
According to the Fatwa of the Standing Committee for Fatwas, “Allah’s Existence is known of necessity to be (part and parcel) of the religion. It is one of the Divine Attributes according to the consensus of Muslims as well as all reasonable people, even the polytheists. Nobody disputes about it except a Dahri [22] A theological term referring either to an atheist or to an adherent of the doctrine that the universe had no beginning in time. heretic. Affirming Allah’s Existence as one of His Attributes does not necessitate that He has a creator because existence is of two modes:
(1) Self-Existence: That is whose existence is independent, thus, it is not obtained from another being. This applies only to Allah, Exalted be He, because His Existence has not been followed by or preceded with or susceptible to non-existence.
(2) Created Existence: This applies to those who came into existence from nothing. This type of existence applies to creatures as they require a creator (i.e. Allah) to bring them into existence.
By this definition, Allah is described as existent according to the first mode, therefore, we express this meaning in our words by saying, “Allah exists.” [23] Fataawa al-Lajinat ad-Daaimah, the first batch, 3/190.
The history of mankind does not record people denying the existence of Allah; it is only an obstinate minority who walked against the current!
Ash-Shahrastaani said, “As for denying the existence of the Creator, the All-Knowing, the Most Capable, and All-Wise, I do not believe it to be a view of anyone reliable and I do not know anyone who holds this view, except for what has been transmitted about a small band of the Dahriyyah that they said, “The world in ancient times was a set of scattered parts that moved randomly, but then coincidentally collided to form the world as we see it today!! Nonetheless, I believe that the person who holds this view does not deny the existence of the Creator but rather acknowledges its existence. This is because the sound innate natures of humans testify that there is a Creator who is All-Wise, All-Knowing and Most Capable. For this reason, it was not dictated upon us to know the existence of the Creator; but we are required to only know Allah’s Oneness and negate partners from Allah.” [24] Nihaayat al-Iqdaam ‘ala ‘Ilm al-Kalaam, p 74.
Ibn Taymiyyah said, “The person who is most famous for championing and professing his denial of the Creator is Pharaoh, although in his heart, he was certain about the existence of the Creator. Allah said: (Musa) said: "Verily, you know that these signs have been sent down by none but the Lord of the heavens and the earth as clear (evidence i.e., proofs of Allah's Oneness and His Omnipotence, etc.). And I think you are, indeed, O Pharaoh, doomed to destruction (away from all good)!” al-Israa: 102 He outwardly displayed the opposite of what his heart believed: And they rejected them, while their inner selves were convinced thereof. an-Naml: 27 [25] Dar’ Ta’arud al-‘Aql Wal Na’ql (8\38, 440)
New terminologies and innovated ways have emerged by some deviated groups such as Jahmis to affirm Allah’s existence.
Ahmad ibn Hanbal mentioned the debate between the Sumaniyyah (those who reject all forms of knowledge except that which is concluded through the five senses) and Jahm ibn Safwaan concerning the existence of Allah. The Sumaniyyah asked Jahm if he had known Allah through any of the five senses. This made Jahm become bewildered and thus did not know what he was worshipping for forty days. Then he redressed this defeat by devising a proof similar to the heretics of the Christians, who claim that the spirit that is within Jesus is the spirit of Allah, from Allah's Essence. Thus, when Allah wants to bring about something, He enters into some of His creation and speaks upon the tongue of that (created being), and thus He commands with whatever He wills and forbids with whatever He wills. But He is a spirit that is absent from (the people's) vision! Further, he interpolated some ayaat of the Quran and rejected the hadeeths of the Prophet (صلى الله عليه وسلم) claiming that whoever describes Allah by anything which He has described Himself with in His Book or on the tongue of His Prophet is a disbeliever and is from those who equate Allah to His creation, causing many people to be misguided and go astray with his words. [26] Ar-Radd ‘ala al-Jahmiyyah, p 93, Dar Ta’aarud al-‘Aql wa an-Naql.
The waves of atheism and heresy that have invaded the Muslim world contributed to the arguing about the Existence, Names, and Attributes of Allah in the censured manner of the people of innovation which is contrary to the way of Allah’s Book and the Sunnah in discussing these issues in a clear, easy, and acceptable manner.
Ibn Taymiyyah debunked the argument of those who made observation and inference through intellect obligatory to be able to attain knowledge of the Creator and commented on it by saying, “This view is not shared by anyone from the righteous predecessors of the Muslims or renowned scholars. Neither it was stated by any Prophet and Messenger, nor it was adopted by all speculative theologians (Mutakallimun), let alone the majority of them. Rather, this is a new view that was introduced into Islam by the speculative theologians of Mu’tazilite and their ilk who the righteous predecessors of the Muslims and renowned scholars unanimously reproached.” [27] Bayaan Talbees al-Jahmiyyah fee Ta?sees Bid’aihim al-kalaamiyyah, 4/570, Al-‘Aqeedah al-Islaamiyyah by ‘Ataaullah Bakhyat al-Mu’aayitah, p 13.