Sahih al-Bukhari, Hadith 3370

Ka`b bin Ujrah met me and said, "Shall I not give you a present I got from the Prophet?" `Abdur- Rahman said, "Yes, give it to me." I said, "We asked Allah's Messenger (ﷺ) saying, 'O Allah's Messenger (ﷺ)! How should one (ask Allah to) send blessings on you, the members of the family, for Allah has taught us how to salute you (in the prayer)?' He said, 'Say: O Allah! Send Your Mercy on Muhammad and on the family of Muhammad, as You sent Your Mercy on Abraham and on the family of Abraham, for You are the Most Praise-worthy, the Most Glorious. O Allah! Send Your Blessings on Muhammad and the family of Muhammad, as You sent your Blessings on Abraham and on the family of Abraham, for You are the Most Praise-worthy, the Most Glorious.'"
Transliteration: "Allahumma Salli ala Muhammadin wa 'ala `Ali Muhammadin, kama sal-laita 'ala all Ibrahima innaka Hamidun Majid. Allahumma barik 'ala Muhammadin wa 'ala all Muhammadin, kama barakta 'ala all Ibrahima, innaka Hamidun Majid."