Musnad Ahmad 32:145

Sufyan narrated to us, from Yahya—it was said to Sufyan, meaning, he heard from Anas, who said: The Prophet, peace and blessings of Allah be upon him, called the Ansar to allot the region of Bahrain to them. They said: "No, not until you allot to our brothers from the Muhajirin the same as [you allot to] us." He said: "You will encounter selfishness after me, so be patient until you meet me."