It is narrated from Sayyiduna Abu Ayyub (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Muzaynah, Juhaynah, Ashja', Aslam, Ghifar and those who are from Banu Ka'b are (our) allies to the exclusion of other people, and Allah and His Messenger are their Protector."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3912