Musnad Abu Ya'la al-Mawsili 129:56

On the authority of Anas, may Allah be pleased with him, that the Emigrants (Muhajirun) came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, we have never seen a people more generous when they have much, nor better in sharing when they have little, than the Helpers (Ansar). We have come to Medina and they have made us partners in the pleasant life. We fear that they will take away all the reward." He said: "No, not as long as you praise them and pray for them."