It is narrated from Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) used to recite in the prayer: 'Allahumma salli 'ala Muhammadin wa 'ala ali Muhammad, kama sallayta 'ala Ibrahima wa 'ala ali Ibrahim, wa barik 'ala Muhammadin wa 'ala ali Muhammad, kama barakta 'ala Ibrahima wa 'ala ali Ibrahim, innaka Hamidun Majid' (O Allah, send down Your mercy upon Muhammad (peace and blessings be upon him) and upon the family of Muhammad too, just as You sent down mercy upon Ibrahim (peace be upon him) and the family of Ibrahim; and send down blessing upon Muhammad (peace and blessings be upon him) and upon his family, just as You sent down blessing upon Ibrahim (peace be upon him) and the family of Ibrahim. Indeed, You are Praiseworthy, Glorious).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2852