Musnad Ahmad 6:16

Muhammad ibn Bishr narrated to us, Mujammi' ibn Yahya al-Ansari narrated to us, Uthman ibn Mawhab narrated to us, from Musa ibn Talhah, from his father, who said: I said: "O Messenger of Allah, how should I send blessings upon you?" He said: "Say: O Allah, send blessings upon Muhammad and upon the family of Muhammad, as You sent blessings upon Ibrahim; indeed, You are Praiseworthy, Glorious. And bless Muhammad and the family of Muhammad, as You blessed the family of Ibrahim; indeed, You are Praiseworthy, Glorious."