Sahih Bukhari Volume 6, Book 60, Hadith Number 320.

Narrated By Ka’b bin Ujra : It was said, “O Allah’s Apostle! We know how to greet you, but how to invoke Allah for you?” The Prophet said, “Say: Allahumma salli ala Muhammadin wa’ala Ali Muhammaddin, kama sallaita ‘ala all Ibrahim, innaka Hamidun Majid.”