Musnad Ahmad 11:0

Narrated by Abu Ubaidah ibn al-Jarrah, whose name is Amir ibn Abdullah, may Allah be pleased with him: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The people of Islam will continue to be protected, and their affairs will continue to be managed by a man from the Quraish, as long as they establish the religion." He said: "And I heard him say: 'The people will continue to be in a state of goodness as long as they have a leader, and if they do not have a leader, they will be in a state of evil.'"