Abdullah bin Isa bin Abd al-Rahman bin Abi Layla (may Allah have mercy on him) says that he heard Abd al-Rahman bin Abi Layla (may Allah have mercy on him) say: I met Ka'b bin Ujrah (may Allah be pleased with him), and he said: Shall I not give you a gift that I heard from the Prophet (peace and blessings be upon him)? I said: Certainly, do give it to me. He said: We asked the Messenger of Allah (peace and blessings be upon him): How should we pray for mercy for your household? He (peace and blessings be upon him) said: "Say: 'Allahumma salli 'ala Muhammadin wa 'ala ali Muhammad, kama sallayta 'ala Ibrahima wa 'ala ali Ibrahim, innaka Hamidun Majid. Allahumma barik 'ala Muhammadin wa 'ala ali Muhammad, kama barakta 'ala Ibrahima wa 'ala ali Ibrahim, innaka Hamidun Majid' (O Allah, send down mercy upon Muhammad (peace and blessings be upon him) and upon the family of Muhammad (peace and blessings be upon him), just as You sent down mercy upon Ibrahim (peace be upon him) and the family of Ibrahim (peace be upon him); indeed, You are Praised, Glorious. O Allah, send down blessing upon Muhammad (peace and blessings be upon him) and upon his family too, just as You sent down blessing upon Ibrahim (peace be upon him) and the family of Ibrahim (peace be upon him); indeed, You are Praised, Glorious)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2856