Musnad Abu Ya'la al-Mawsili 117:63

Suwayd ibn Sa'id narrated to us, Zakariyya ibn Yahya al-Dhari' narrated to us, from Thabit al-Bunani, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to say: "O Allah, indeed the good is the good of the Hereafter, so forgive the Ansar and the Muhajirun."