[Ibn Taymiyyah’s Comment]
I say:

There is no need for this question or its answer, given our immediate knowledge that an agent acting upon something existent must itself exist. More than one speculative thinker had already anticipated him in this.

[Al-Juwaynī’s Words in al-Irshād]
Such was Abū al-Ma‘ālī al-Juwaynī, who said in al-Irshād:

“If someone says, ‘In your preceding discussion, you have established knowledge of the Maker. Why, then, do you object to someone who supposes the Maker to be nonexistent?’ we reply: ‘Nonexistence, according to us, is pure negation. The nonexistent possesses no affirmative attribute. There is no difference between denying the Maker and supposing the Maker to be nonexistent in every respect. Indeed, although denying the Maker is invalidated by decisive proof, that position is not internally contradictory. Affirming a Maker who does not exist, however, is contradictory. The notion of a nonexistent Maker is a necessary consequence only for the Mu‘tazilites, since they ascribe affirmative attributes to the nonexistent and hold that it possesses the distinctive properties of genera.’”

He said:

“The correct approach is not to count existence among the attributes, for existence is the essence itself. It is not comparable to a substance’s occupying space, since occupying space is an attribute additional to the substance’s essence. According to us, the existence of a substance is the substance itself, without positing anything additional.”

He said:

“The leading scholars use the term ‘attributes’ broadly when counting existence among them; knowledge of existence is knowledge of the essence.”

Al-Kiyā al-Harrāsī al-Tabarī said:

“When we say that the Creator exists, His existence is His essence. Our colleagues agree on this, both those who affirm states and those who deny them, except according to the view of the Mu‘tazilites, who said: ‘The nonexistent is a thing.’”