Sahih al-Bukhari, Book 62, Hadith 8 (In-Book) ⓘ
Narrated Ibn `Abbas: The Prophet said, "If I were to take a Khalil, I would have taken Abu Bakr, but he is my brother and my companion (in Islam).
حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا وُهَيْبٌ، حَدَّثَنَا أَيُّوبُ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " وَلَوْ كُنْتُ مُتَّخِذًا مِنْ أُمَّتِي خَلِيلاً لاَتَّخَذْتُ، أَبَا بَكْرٍ وَلَكِنْ أَخِي وَصَاحِبِي " .
also referenced under: Hadith 3656 (DarusSalam) & Volume 5, Book 57, Hadith 8 (USC-MSA)