Sayyiduna Anas (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said: "The Imams (leaders) are from Quraysh. When they judge, they are just; when they are asked for mercy, they show mercy; and when they make a covenant, they fulfil it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16542