Narrated Abu Bakr Abu Bakr As Siddiq (Arabic ابو بكر الصديق, alternative spellings, Abubakar, Abi Bakr, Abu Bakar) (c. ...
I was with the Prophet in the Cave. When I raised my head, I saw the feet of the people. I said, "O Allah's Apostle! If some of them should look down, they will see us." The Prophet said, "O Abu Bakr, be quiet! (For we are) two and Allah is the Third of us." Sahih Bukhari 58.259
Sahih Bukhari is one of the Sunni Six Major Hadith collections, collected by Muhammad al-Bukhari who spent 16 years writing it. ...
Qur'an
[9.40] If you will not aid him, Allah certainly aided him when those who disbelieved expelled him, he being the second of the two, when they were both in the cave, when he said to his companion: Grieve not, surely Allah is with us. So Allah sent down His tranquillity upon him and strengthened him with hosts which you did not see, and made lowest the word of those who disbelieved; and the word of Allah, that is the highest; and Allah is Mighty, Wise.