Sahih Muslim Book 1, Hadith Number 140.

Chapter : The love of Ansar (helpers) and ‘All (may Allah be pleased with all of them) is (an Ingredient) of Iman and (one of) its signs, and hatred against them is a sign of dissemblance.

It is narrated on the authority of Abu Sa’id Khudri that the Messenger of Allah observed: The person who believes in Allah and the Last Day never nurses a grudge against the Ansar.