The Messenger of Allah ﷺ said, "People will not cease questioning until they say, 'This is Allah, the Creator of everything, so who created Allah?'"
قال رسول الله ﷺ: لن يبرح الناس يتساءلون حتى يقولوا: هذا الله خالق كل شيء، فمن خلق الله؟
Bukhari narrated it in the Book of Holding Fast (7296) from Hasan bin Sabbah, he said, Shababa narrated to us, Warqa narrated to us, from Abdullah bin Abdul-Rahman, who said, I heard Anas bin Malik, and he mentioned it. Muslim also narrated it in the Book of Faith (136) from another route from Anas, with similar wording.