We don’t reply/give Salam during Namaz. What are the other activities when we should not give/reply to Salam?
بسم الله الرحمن الرحيم
One should not greet a person who is busy in salah, khutbah, tilawat, dhikr, or eating food or morsel is in his mouth or defecates or is busy in azan, iqamah, dua etc. If someone greets him, then it is not wajib for him to respond.
Allah knows Best!
Darul Uloom Deoband