The Messenger of Allah ﷺ said, "People will keep questioning one another until it is said, 'Allah created creation, so who created Allah?' Whoever finds anything of that within himself, let him say, 'I believe in Allah.'"
حدثنا هارون بن معروف حدثنا سفيان عن هشام عن أبيه
قال رسول الله ﷺ لا يزال الناس يتساءلون حتى يقال هذا خلق الله الخلق فمن خلق الله فمن وجد من ذلك شيئا فليقل آمنت بالله
Muslim narrated it in the Book of Faith, chapter on describing insinuating thoughts about faith and what one who experiences them should say, hadith no. 134, from Harun bin Maruf with this chain. Bukhari also narrated it, hadith no. 3276, through another route from Urwa Abu Hisham with this chain.