Shaykhu'l-Islam Ibn Taymiyyah said, “The Tawhid with which the Messengers came with comprises of affirming that Divinity and worship belong to Allah alone, such that a person witnesses that none has the right to be worshipped except Allah, and that none is worshipped except Him, nor depended upon other than Him, nor are alliances or enemies made except for Him, nor is an action done except for Him. This affirmation also covers those Names and Attributes which Allah affirms for Himself, as Allah (awj) says:
“And the Allah to be worshipped is only one Allah. None has the right to be worshipped except Him, the Most Merciful, the Bestower of Mercy.” (ali Imran 3/163) And Allah (awj) says:
“Do not take two objects of worship. Indeed, Allah is the only Deity to be worshipped, so fear Him.” (an-Nahl 16/51) And He (swt) says:
“Whosoever calls upon (i.e. supplicates or prays to) other than Allah, for which he has no proof, then his reckoning is only with his Lord. Indeed, the disbelievers will not be successful.” (Mu‘minun 23/117) Allah (swt) also says:
“And ask those of our Messengers whom we sent before you, Did We ever appoint objects of worship besides the Most Merciful?” (az-Zukhruf 43/45) And Allah (awj) informed us about every Prophet from amongst the Prophets that they called the people to the worship of Allah alone, having no partner, as He (awj) said:
“Indeed there is an excellent example for you in Ibrahim and those with him, when they said to their people: Indeed we are free from you and whatever you worship besides Allah. We have rejected you, and there has arisen between us and you, hostility and hatred forever - until you believe in Allah alone.” (al-Mumtahia 60/4) And Allah (swt) said about the mushriks:
“When it is said to them: None has the right to be worshipped except Allah, they become arrogant. And they say: Are we to abandon those deities that we worship because of a mad poet?” (as-Saffat 37/35-36) And this occurs a lot in the Qur‘an.
And what is meant by Tawhid is not merely Tawhid ar-Rububiyyah -the belief that Allah alone is the Creator- which is what some of the people of Kalaam and the Sufis think! So they think that if they affirm this type of Tawhid, along with its proofs, then they have affirmed the utmost limits of Tawhid and that if they bear witness to this and become absorbed in it, then they have absorbed themselves in the limits of Tawhid! However, this is not the case. Since even if a person agreed to those attributes which are befitting to the Lord, and declared Him free from everything He should be declared free from and affirmed that He alone is the creator of everything -then still such a person would not be a muwahhid until along with this, he witnesses that the only Ilah (i.e. object of worship) is Allah- (i.e. none has the right to he worshipped except Allah alone)- affirming that Allah alone is the Ilah deserving off all worship, adhering to this worship and associating no partners with Him. Also affirming that this Ilah is He who is deified and worshipped and who deserves worship and it is not that Ilah merely with the meaning, “The One who has the power to create and originate."
So if an explainer (of the Qur‘an) explains Ilah to mean, “The One who has the power to create and originate” and believes that this is the most particular description of Ilah and affirms this to be the limits of Tawhid -as is done by the people of Kalaam, and it is what they say from Abu'l-Hasan al-Ash’ari and his followers- then they do not know the true reality of the Tawhid with which Allah sent His Messengers, since the Arab mushriks used to agree that Allah alone is the Creator of everything. Yet despite this, they were still mushriks, as Allah (swt) says: “Most people do not believe in Allah except that they commit shirk (i.e. associate others with Him in belief and worship).” (Yusuf 12/106)
A group from amongst the salaf said: “If you ask them who created the Heavens and the earth, they will say, ‘Allah’ - yet along with this, they worshipped others besides Him.” (narrated from Ibn Abbas (ra) and others; Tabari, Jaami’ul-Bayan an Ta’wilu'l-Qur‘an, 13/50-51) Allah (swt) said:
“Say: ‘Whose is the earth and all that is in it, if you do indeed know?’ They will say, ‘It belongs to Allah.’ Say, ‘Will you not then remember?’ Say, ‘Who is the Lord of the heavens and the Lord of the great Throne?’ They will say, ‘Allah.’ Say, ‘Will you not then fear Him?’” (Mu'minun 23/84-87) So not everyone who affirms that Allah is the Lord of everything and is its Creator, will be a worshipper of Him to the exclusion of everything else -calling upon Him alone, hoping in Him alone, having fear of Him alone, forming allegiance and enmity for Him, obeying His Messengers, ordering what He orders and forbidding what He forbade.”
(Majmua al-Fatawa, 3/97-105)