If I am during the midst of any part of a mustahab or wajib prayer and somebody takes the name of the Prophet of Islam, according to Ayatollah Wahid, do I have to stop the qiraat and recite salwaat on him?

Saying salawat on the Prophet and his progeny is mustahab when his name is mentioned, and it would not break the salaah, so there’s no harm in saying it, however it is not necessary.