Musnad Ahmad 30:3826

Kathir narrated to us, Ja'far narrated to us, Yazid ibn al-Asamm narrated to us, from Abu Hurayrah, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "People will surely ask you about everything, until they say: 'Allah created everything, so who created Him?'" Yazid said: Najbah ibn Sabigh al-Sulami narrated to me that he saw a caravan that came to Abu Hurayrah and asked him about that. He said: "Allah is the Greatest! My intimate friend did not tell me anything except that I have seen it and I am awaiting it." Ja'far said: It reached me that the Prophet, peace and blessings of Allah be upon him, said: "If people ask you about this, then say: 'Allah was before everything, and Allah created everything, and Allah will be after everything.'"