It is narrated from Sayyiduna Abu Humayd al-Sa'idi (may Allah be pleased with him) that the Companions (may Allah be pleased with them) said: "O Messenger of Allah (peace and blessings be upon him), how should we send blessings upon you?" He (peace and blessings be upon him) said: "Say: 'Allahumma salli 'ala Muhammadin wa azwajihi wa dhurriyyatihi, kama sallayta 'ala Ibrahim, wa barik 'ala Muhammadin wa azwajihi wa dhurriyyatihi, kama barakta 'ala Ibrahim, innaka Hamidun Majid' (O Allah, send Your mercy upon Muhammad (peace and blessings be upon him), his wives and his offspring, as You sent Your mercy upon Ibrahim; and send Your blessings upon Muhammad (peace and blessings be upon him), his wives and his offspring, as You sent Your blessings upon Ibrahim. Indeed, You are the Most Praiseworthy, the Most Glorious)."
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Imam Malik (may Allah have mercy on him) through Abdullah and Muhammad (the sons of Abu Bakr) except Isa (may Allah have mercy on him), whereas the narrators generally narrated it from Imam Malik (may Allah have mercy on him) through Muhammad bin Abi Bakr alone."
Hadith Referenceالمعجم الأوسط / باب الألف / 1652
Hadith Takhrij«أخرجه البخاري فى «صحيحه» برقم: 3369، 6360، ومسلم فى «صحيحه» برقم: 407، ومالك فى «الموطأ» برقم: 572 / 172، والنسائي فى «المجتبى» برقم: 1293 / 1، والنسائي فى «السنن الكبرى» برقم: 1218، 9804، 11103، وأبو داود فى «سننه» برقم: 979، وابن ماجه فى «سننه» برقم: 905، والبيهقي فى «السنن الكبرى» برقم: 2907، 2908، 2909، وأحمد فى «مسنده» برقم: 24087، والطحاوي فى «شرح مشكل الآثار» برقم: 2238»