Musnad Ahmad 32:942

Yahya narrated to us, from Yahya ibn Sa’id, who said: I heard Anas ibn Malik narrating that the Messenger of Allah (may Allah bless him and grant him peace) intended to write a document for some people of the Ansar regarding Bahrain. They said: "No, unless you write the same for our brothers from the Muhajirun." So he called them, but they refused. He said: "As for you, you will see selfishness after me, so be patient until you meet me."