What lesson did the Prophet Muhammad (saw) teach the Ansar when he 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"?
 Narrated 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, Sa`d (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."