From Sahih Bukhari (Hadith 467):
Narrated Ibn `Abbas:"Allah's Messenger (ﷺ) in his fatal illness came out with a piece of cloth tied round his head and sat on the pulpit. After thanking and praising Allah he said, "There is no one who had done more favor to me with life and property than Abu Bakr bin Abi Quhafa. If I were to take a Khalil, I would certainly have taken Abu- Bakr but the Islamic brotherhood is superior. Close all the small doors in this mosque except that of Abu Bakr
Reference: Bukhari 467