It is narrated from the Mother of the Believers Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "If I were to take (anyone) as my khalil (intimate friend), I would certainly have taken Sayyiduna Abu Bakr (may Allah be pleased with him) as my khalil; but the brotherhood of Islam is the most excellent."
In the printed edition of Dar al-Haramayn it is like this (the name Ali), and the correct name is probably Mu'alla, as in "Sharh Mushkil al-Athar".
Hadith Referenceالمعجم الأوسط / باب الألف / 2055
Hadith Gradingمحدثین:فيه علي بن عبد الرحمن الواسطي لم يُعرف
Hadith Takhrij«قال الهيثمي: فيه علي بن عبد الرحمن الواسطي ولم أعرفه «مجمع الزوائد ومنبع الفوائد، ج 9، ص 44»»