It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "No one has done me a favour equal to the favour of Abu Bakr. He gave me his daughter in marriage and took me out to the abode of emigration (Madinah). If I were to take anyone as a khalil (intimate friend), I would have taken Abu Bakr, but (between us) is a brotherhood of religious love that will last until the Day of Resurrection."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12593