From Sahih Bukhari (Hadith 4663):
Narrated Abu Bakr:I was in the company of the Prophet (ﷺ) in the cave, and on seeing the traces of the pagans, I said, "O Allah's Messenger (ﷺ) If one of them (pagans) should lift up his foot, he will see us." He said, "What do you think of two, the third of whom is Allah?
Reference: Bukhari 4663