They asked the Messenger of Allah ﷺ, "How shall we send blessings upon you?"He replied, "Say, 'O Allah, send blessings upon Muhammad and bless Muhammad and the family of Muhammad, just as You sent blessings and blessed Ibrahim and the family of Ibrahim among the worlds. Indeed, You are Praiseworthy, Glorious.' And the salutation is as you have already been taught."
سألوا رسول الله ﷺ كيف نصلي عليك؟ قال: قولوا: اللهم صل على محمد وبارك على محمد وعلى آل محمد، كما صليت وباركت على إبراهيم وآل إبراهيم في العالمين، إنك حميد مجيد، والسلام كما علمتم.
Bazzar narrated it in Kashf Astar (565) from Ahmad bin Abdah, from Salim bin Akhdar, from Dawud bin Qays, from Nuaym, from Abu Hurairah, who mentioned the hadith. Hafiz said in Nataij Afkar (2/208), "This hadith is sahih."Abu Dawud (982) also narrated it from Abu Hurairah with a different chain, and its wording differs slightly, and there is some criticism of its chain.There are other hadiths on this subject mentioned in the book on prayer.