The Messenger of Allah ﷺ said, "You will go on questioning until one of you says, 'Here is Allah, who created all creation, so who created Allah?'"
وقال رسول الله ﷺ لا تزالون تستفتون حتى يقول أحدكم هذا الله خلق الخلق فمن خلق الله عز وجل
It is sahih due to the soundness of the Sahifah. It appears in the individual Sahifah, numbered 93, placed before the preceding hadith 8191, and the two sheikhs (Bukhari and Muslim) did not narrate it through this route. Its meaning is established through other channels, as already passed at 7777 through the narration of Muhammad bin Sirin from Abu Hurairah, and we noted this there, as well as the narration of it by the two sheikhs through a route other than that of Hammam.