The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fada'il Al-Sahabah)
Muslim :: Book 31 : Hadith 6104
Abu Usaid reported Allah's Messenger (may peace be upon him) as saying: The worthiest clans of the Ansar are Banu Najjar, thereafter Banu al-Ashhal; thereafter Banu Harith b. Banu Khazraj; thereafter Banu Sa'idah and there is goodness in all clans of the Ansar. Sa'd said: I see that he (the Holy Prophet) has placed others above us. It was said to (him): He has placed you above many others.