Musnad Ahmad 25:770

Musa ibn Dawud narrated to us, Abd al-Rahman ibn al-Ghasil narrated to us, from Ikrimah, from Ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) came out covering his head with his garment and said: "O people, the people will increase, and the Ansar will decrease. So whoever among you is in charge of a matter in which he can benefit anyone, let him accept from their good-doers and overlook their wrongdoers."