We said, "Messenger of Allah, we know how to greet you with peace, but how do we send blessings upon you?"He replied, "Say, O Allah, send blessings upon Muhammad, Your servant and Messenger, as You sent blessings upon Ibrahim, and bless Muhammad and the family of Muhammad as You blessed Ibrahim."
أخبرنا قتيبة قال حدثنا بكر وهو ابن مضر عن ابن الهاد عن عبد الله بن خباب
قلنا يا رسول الله السلام عليك قد عرفناه فكيف الصلاة عليك قال قولوا اللهم صل على محمد عبدك ورسولك كما صليت على إبراهيم وبارك على محمد وآل محمد كما باركت على إبراهيم
Bukhari narrated it in the Book of Tafsir, chapter on His saying, "Indeed, Allah and His angels send blessings on the Prophet", Bukhari: 4798, and Bukhari: 6358, from the hadith of Yazid bin Abdullah bin Had, through him. It is also found in Al-Kubra, hadith: 1216.