Sahih Bukhari Volume 5, Book 58, Hadith Number 133.

Narated By Abu Usaid : The Prophet said, “The best of the Ansar’s families (homes) are those of Banu An-Najjar and then (those of) Banu ‘Abdul Ash-hal, then (those of) Banu Al-Harith bin Al-Khazraj and then (those of) Banu Sa’ida; nevertheless, there is good in all the families (houses) of the Ansar.” On this, Sad (bin Ubada) said, “I see that the Prophet has preferred some people to us.” Somebody said (to him), “No, but he has given you superiority to many.”