It is narrated from Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) that a man said: O Messenger of Allah! We have learned how to send salam upon you, so how should we send blessings upon you? He (peace and blessings be upon him) said: "Say: O Allah! Send blessings upon Muhammad and the family of Muhammad, as You sent blessings upon Ibrahim; indeed, You are Praiseworthy, Glorious. O Allah! Send Your favour (barakah) upon Muhammad and the family of Muhammad, as You sent Your favour upon Ibrahim; indeed, You are Praiseworthy, Glorious."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16316