Allah’s saying: “Indeed, Allah and His angels send blessings upon the Prophet...” (Surah Ahzab: 56

Narrated Abu Sa'id Al-Khudri (may Allah be pleased with him): We said to the Messenger of Allah (peace and blessings of Allah be upon him), "O Messenger of Allah! We know how to send Salam upon you, but how should we send Salat upon you?" He (peace be upon him) said: "Say: O Allah! Send mercy upon Muhammad (peace be upon him), Your servant and Messenger, as You sent mercy upon Ibrahim (peace be upon him). And send blessings upon Muhammad (peace be upon him) and upon the family of Muhammad, as You sent blessings upon Ibrahim (peace be upon him)."

Narrated from Sayyiduna Ka’b bin ‘Ujrah (may Allah be pleased with him) that (the Companions) said, “O Messenger of Allah! We have learned how to send peace upon you (i.e., it is recited in at-Tahiyyat), but how should we send blessings (salat) upon you?” The Prophet (peace and blessings be upon him) said: “Say: O Allah! Send mercy upon Muhammad (peace be upon him) and upon the family of Muhammad, as You sent mercy upon the family of Ibrahim (peace be upon him). Indeed, You are Praiseworthy and Glorious. (And) O Allah! Send blessings upon Muhammad (peace be upon him) and upon the family of Muhammad, as You sent blessings upon the family of Ibrahim (peace be upon him). Indeed, You are Praiseworthy and Glorious.”