Musnad Ahmad 980:2

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Isma'il ibn Raja', from Aws ibn Dam'aj, from Abu Mas'ud al-Ansari, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The one who leads the people in prayer is the one among them who is most proficient in the Book of Allah. If they are equal in recitation, then the one among them who is most knowledgeable of the Sunnah. If they are equal in the Sunnah, then the one among them who migrated first. If they are equal in migration, then the oldest of them in age. And do not lead a man in his authority, and do not sit on his place of honor in his house unless he gives you permission."