Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) said something harsh to Sayyiduna Umar (may Allah be pleased with him), then said: "My brother, seek forgiveness for me." Sayyiduna Umar (may Allah be pleased with him) became angry. He repeated this several times, but Umar's (may Allah be pleased with him) anger only grew, so he mentioned it to the Prophet (peace and blessings be upon him), and both of them came to him (peace and blessings be upon him) and sat down. The Messenger of Allah (peace and blessings be upon him) said: "Your brother asks you to seek forgiveness for him, and you refuse?" Sayyiduna Umar (may Allah be pleased with him) said: "By the One who sent you with the truth as a Prophet, every time he asked me, I have been seeking forgiveness for him, and after you there is no one among Allah's creation more beloved to me than him." Sayyiduna Abu Bakr (may Allah be pleased with him) said: "And by the One who sent you with the truth, after you there is no one more beloved to me than him either." Thereupon the Messenger of Allah (peace and blessings be upon him) said: "Do not hurt me concerning my companion, for Allah, the Mighty and Majestic, sent me with guidance and the religion of truth, and you said: 'You have lied,' while Abu Bakr said: 'You have spoken the truth.' Had Allah, the Mighty and Majestic, not called him a companion (sahib), I would have taken him as my khalil (intimate friend), but this is brotherhood for the sake of Allah. Listen! Close every door except the door of Ibn Abi Quhafah."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13326