Musannaf Ibn Abi Shayba 27:739

Al-Fadl ibn Dukayn narrated to us, he said: Ibn al-Ghasil narrated to us, he said: Ikrimah narrated to us, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) sat one day upon the pulpit, wearing a cloak, wrapped in it, having bound his head with a dark-colored headband. He praised Allah and extolled Him, then said: "O people, you will increase, and the Ansar will decrease until they are like salt in food. So whoever is entrusted with any of their affairs, let him accept from their doer of good, and let him overlook their wrongdoer."