(2) باب مَنَاقِبِ الْمُهَاجِرِينَ وَفَضْلِهِمْ
Narrated Abu Bakr:
I said to the Prophet (ﷺ) while I was in the Cave. "If any of them should look under his feet, he would see us." He said, "O Abu Bakr! What do you think of two (persons) the third of whom is Allah?"
Reference: Sahih al-Bukhari 3653
In-book reference: Book 62, Hadith 5
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 57, Hadith 5