Musnad Abu Ya'la al-Mawsili 122:1

Al-Hasan ibn Isma'il Abu Sa'id narrated to us in Basra, Ibrahim ibn Sa'd narrated to us, from his father, from Anas, may Allah be pleased with him, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The leaders are from Quraysh; if they judge, they are just; if they make a covenant, they fulfill it; and if they are asked for mercy, they show mercy."