Musnad Abu Ya'la al-Mawsili 136:2

Abu Bakr narrated to us, Waki' narrated to us, al-A'mash narrated to us, Sahl Abu al-Aswad narrated to us, from Bukayr al-Jazari, from Anas, who said: The Messenger of Allah came to us while we were in the house of a man from the Ansar. He took hold of the two doorposts and then said: "The leaders are from Quraysh. They have a right over you, and you have the like of that over them, provided that when they judge, they act justly; when they are asked for mercy, they show mercy; and when they make a covenant, they fulfill it. Whoever among them does not do that, then upon him is the curse of Allah, the angels, and all of mankind."