Sahih Bukhari Volume 6, Book 60, Hadith Number 321.

Narrated By Abu Said Al-Khudri : We said, “O Allah’s Apostle! (We know) this greeting (to you) but how shall we invoke Allah for you?” He said, “Say! Allahumma salli ala Muhammadin ‘Abdika wa rasulika kama- sallaita ‘ala all Ibrahim wa barik ala Muhammadin wa’ala all Muhammadin kama barakta ‘ala all Ibrahim.’ Al-Laith said: ‘Ala Muhammadin wa ‘ala all Muhammadin kama barakta ala all Ibrahim.