Sahih Bukhari Volume 5, Book 58, Hadith Number 132.

Narated By Abu Hamza : (A man from the Ansar) The Ansar said, “Every nation has followers and (O Prophet) we have followed you, so invoke Allah to let our followers be considered from us (as Ansar like ourselves).” So the Prophet said, “O Allah! Let their followers be considered as Ansar like themselves.”