Sahih Muslim Book 5, Hadith Number 2306.

Chapter : The Khwarij and their characteristics.

Anas b. Malik reported that the Messenger of Allah (may peace be upon him) gathered the Ansar and said: Is there someone alien among you? They said: No, but only the son of our sister. Upon this the Messenger of Allah (may peace be upon him) said: The son of the sister of the people is included among the tribe, and (farther) said: The Quraish have recently abandoned Jahillyya and have just been delivered from distress; I, therefore, intend to help them and conciliate them. Don’t you feel happy that the people should return with worldly riches and you return with the Messenger of Allah to your houses? (So far as my love for you is concerned I should say) if the people were to tread a valley and the Ansar tread a narrow path (in a mountain) I would tread the narrow path of the Ansar.