What the instruction actually was
Notice how short the prescribed response is. The Qur'an says that when a suggestion comes from Shaytan, seek refuge in Allah, and that is the whole instruction. And when the Prophet, peace be upon him, was told about the thought that ends in but who created Allah, what he gave was one line to say. Not an argument, and not an investigation.
Qur’an and Sunnah
وَإِمَّا يَنزَغَنَّكَ مِنَ ٱلشَّيۡطَٰنِ نَزۡغࣱ فَٱسۡتَعِذۡ بِٱللَّهِۖ إِنَّهُۥ هُوَ ٱلسَّمِيعُ ٱلۡعَلِيمُ
If a prompting from Satan should stir you, seek refuge with God: He is the All Hearing and the All Knowing
Qur’an 41:36
وَإِمَّا يَنزَغَنَّكَ مِنَ ٱلشَّيۡطَٰنِ نَزۡغࣱ فَٱسۡتَعِذۡ بِٱللَّهِۚ إِنَّهُۥ سَمِيعٌ عَلِيمٌ
If Satan should prompt you to do something, seek refuge with God- He is all hearing, all knowing
Qur’an 7:200
Narrated Safiya bint Huyay:While Allah's Messenger (ﷺ) was in I`tikaf, I called on him at night and having had a talk with him, I got up to depart. He got up also to accompany me to my dwelling place, which was then in the house of Usama bin Zaid. Two Ansari men passed by, and when they saw the Prophet (ﷺ) they hastened away. The Prophet said (to them). "Don't hurry! It is Safiya, the daughter of Huyay (i.e. my wife)." They said, "Glorified be Allah! O Allah's Messenger (ﷺ)! (How dare we suspect you?)" He said, "Satan circulates in the human mind as blood circulates in it, and I was afraid that Satan might throw an evil thought (or something) into your hearts
Sahih al-Bukhari 3281graded sound, sahihaynfull report
It is narrated on the authority of Abu Huraira that some people from amongst the Companions of the Apostle (ﷺ) came to him and said:Verily we perceive in our minds that which every one of us considers it too grave to express. He (the Holy Prophet) said: Do you really perceive it? They said: Yes. Upon this he remarked: That is the faith manifest
Sahih Muslim 132graded sound, sahihaynfull report
It is narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said:Men will continue to question one another till this is propounded: Allah created all things but who created Allah? He who found himself confronted with such a situation should say: I affirm my faith in Allah
Sahih Muslim 134graded sound, sahihaynfull report
Translation: M.A.S. Abdel Haleem, The Qur'an, Oxford University Press, 2004.