Sayyiduna Anas (may Allah be pleased with him) said: the Prophet (peace and blessings be upon him) came to us while we were sitting in a house with a group of the Muhajirun. Every one of us began making room beside himself, hoping that the Prophet (peace and blessings be upon him) would sit next to him, but he (peace and blessings be upon him) stood at the door and said: "The Imams (leaders) will be from Quraysh, and just as I have a great right over you, they too have the like of it, as long as they do three things: when they are asked for mercy, they show mercy; when they judge, they are just; and when they make a covenant, they fulfil it. Whoever of them does not do that, upon him is the curse of Allah, the angels and all the people."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16541