From Sahih Muslim (Hadith 1306):
Abu Rafi' reported:I saw Abu Huraira performing prostration (while reciting this verse: )" When the heaven burst asunder." I said to him: Do you prostrate yourself (while reciting) i? He said: Yes, I saw my best Friend (ﷺ) prostrating himself on (the recital of this verse) and I shall continue prostrating till I meet him. Shu'ba asked: Do you mean (by Friend) the Messenger of Allah (ﷺ)? He said: Yes
Reference: Muslim 1306