Sunan At-Tirmidhi

Narrated Anas:that Abu Bakr narrated to him, he said: ""While were in the cave, I said to the Prophet (ﷺ): 'If one of them were to look down at his feet, then he would see us under his feet.' So he said: 'O Abu Bakr! What do you think about two, the third of whom is Allah?