Musnad Ahmad 789:19

'Affan narrated to us, Sakin bin 'Abd al-'Aziz narrated to us, Sayyar bin Salamah Abu al-Minhal narrated to us, he said: I entered with my father upon Abu Barzah, and I had two earrings in my ears that day, and I was a young boy. He said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The leaders are from Quraysh, for three things, as long as they do three things: if they judge, they act justly; if they are asked for mercy, they show mercy; and if 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."