The message of Allah Ta'ala to Sayyiduna Rasoolullah (sallal laahu alaihi wasallam) has come down to us in the form of the Holy Quran and the teachings of Sayyiduna Rasoolullah (sallal laahu alaihi wasallam) have reached us in the form of the Ahadith.
Let us see what both the Holy Quran and Ahadith say about Durood Shareef (Salawat):
INNAL LLAHA WA MALAA'IKATAHU YU SALLUNA ALLAN NABIYI. YA AYYUHAL LAZEENA AAMANU SALLU ALAIHI WASALLIMU TASLEEMA.
Almighty Allah says: "Surely Allah and His Angels send blessings on the Holy Prophet (sallal laahu alaihi wasallam). O you who believe! Send Blessings (Durood) and Salutations (Salaams) on the Prophet with worthy Salutation". (Surah al-Ahzab: 56).
In this verse of the Holy Quran, Almighty Allah, His Malaa'ikah and the Muslims have been mentioned as sending Durood upon Sayyiduna Rasoolullah (sallal laahu alaihi wasallam).