Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"I heard Ibn Abi Laila say: 'Kab bin Ujrah met me and said: "Shall I not give you a gift? The Messenger of Allah (saw) came out to us and we said: 'We know what it means to send greetings on you, but what does it mean to send peace and blessings upon you?' He said: 'Say: Allahumma salli 'ala Muhammad (SAW)in wa 'ala ali Muhammad (SAW)in, kama sallayta 'ala Ibrahima, innaka Hamidun Majid; Allahumma barik 'ala Muhammad (SAW)in wa 'ala ali Ibrahima, innaka Hamidun Majid (O Allah, send your grace, honour and mercy upon Muhammad (SAW) and upon the family of Muhammad (SAW), as You sent Your grace, honour and mercy upon Ibrahim, You are indeed Praiseworthy, Most Glorious. O Allah, send Your blessings upon Muhammad (SAW) and the family of Muhammad (SAW), as You sent Your blessings upon Ibrahim, You are indeed Praiseworthy, Most Glorious).'" (Sahih)