Musnad Ahmad 6:15

It was narrated from Moosa bin Talhah, that his father said:

I said: “O Messenger of Allah(ﷺ), how do we send blessings upon you?” He said: `Say: O Allah, send Your salah (grace, honour and mercy) upon Muhammad and upon the family of Muhammad, as You sent Your salah upon the family of Ibrahim, You are indeed Praiseworthy, Most Glorious. And send Your blessings upon Muhammad and the family of Muhammad, as You sent Your blessings upon the family of Ibrahim, You are indeed Praiseworthy, Most Glorious.”