مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4134
Musnad of Abdullah bin Mas'ood
It was narrated from ‘Abdullah from the Prophet (ﷺ) that He said: "If I were to take anyone among my ummah as a close friend, I would have taken Abu Bakr as a close friend."
Musnad Ahmad 4161Its isnad is saheeh, Muslim (2383)]