Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) said (to Abd al-Rahman bin Abi Layla (may Allah have mercy on him)): Shall I not give you a gift? I said: "Certainly." He said: We said: "O Messenger of Allah, we have learned how to send salutations upon you; so how shall we send blessings upon you?" He (peace and blessings be upon him) said: "Say: O Allah, send down Your mercy upon Muhammad and the family of Muhammad as You sent down Your mercy upon Ibrahim; indeed, You are the Praised, the Glorious. And send down Your blessings upon Muhammad and the family of Muhammad as You sent down Your blessings upon Ibrahim and the family of Ibrahim; indeed, You are the Praised, the Glorious."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16334