Anas bin Malik reported,
The Messenger of Allah ﷺ said, "People will keep questioning one another until they say, 'This is Allah, the Creator of all things, so who created Allah?'"In another wording from him, the Messenger of Allah ﷺ said, Allah 
said, "Your nation will keep saying, 'What is this? What is that?' until they say, 'This is Allah who created creation, so who created Allah?'"
Azami 15024
Sahihعن أنس بن مالك قال
قال رسول الله ﷺ: لن يبرح الناس يتساءلون حتى يقولوا: هذا الله خالق كل شيء، فمن خلق الله وفي لفظ عنه: عن رسول الله ﷺ قال: قال الله عز وجل: إن أمتك لا يزالون يقولون: ما كذا؟ ما كذا؟ حتى يقولوا: هذا الله خلق الخلق فمن خلق الله.
Bukhari narrated it in the Book of Holding Fast (7296), from Hasan bin Sabbah, who said, Shababa narrated to us, Warqa narrated to us, from Abdullah bin Abdul-Rahman, who said, I heard Anas bin Malik say, then he related it.Muslim narrated it in the Book of Faith (136), through several routes from Mukhtar bin Fulful, from Anas bin Malik, who related it with the second wording.