Another gem from Imam Abu Bakr al-Mulla’s commentary Minhaj al-Raghib:
“Know that sending salutations upon Him (Allah bless him and give him peace) is compulsory (wajib). There are varying opinions as to when it is compulsory.
One: After the last tashahhud of every prayer according to the Shafi scholars.
Two: After accepting Islam during ones lifetime, atleast once.
Three: Everytime He (Allah bless him and give him peace) is mentioned, this was the view of al-Halimi from the Shafis, al-Lakhami from the Malikis, al-Tahawi from the Hanafis, and Ibn Battah from the Hanbalis.
Four: In every gathering.
Five: At the beginning and end of every supplication/dua. See Sharh al-Safawi Ala al-Zubad.”