"Allah sends His Salah on the Prophet, and also His angels (do so). O you who believe! Send your Salah on him, and greet him with Taslim." (Al Quran, 33:56)"
“The heaviest thing to be placed on the scales on the Day of Resurrection is the invocation of blessings on Muhammad and his household.”
Imam Muhammad al-Baqir (ع) Biharul Anwar v. 94, p. 49, no. 9