In the name of Allah
One praying responds to salams with a hand gesture. This is the position of the majority: the Malikis, Shafi`is, and Hanbalis. Most scholars are of this view. The majority of scholars including Shafi say that it is not Makrooh to reply the greetings while one is praying but it is desirable to do so. There is a strong opinion in the Maliki school that it is wajib to reply to salams with gestures while praying. The Hanafis differ. They claim it is makruh to greet someone who is praying and reply to the greeting, even with a gesture. It is stated in the Hanafi book Nur al Idah:
‘’Replying to someone’s salaam with the tongue or by shaking hands renders the prayer void, even if one does so forgetfully. However, a gesture without shaking hands or talking is disliked.’’[i]
The Messenger of Allah (ﷺ) sent me on an errand. I (having done the business assigned to me came back and) joined him as he was going (on a ride). Qutaiba said that he was saying prayer while he rode. I greeted him. He gestured to me. When he completed the prayer. he called me and said: You greeted me just now while I was engaged in prayer. (Qutaiba said): His (Prophet’s face) was towards the east, as he was praying.’’[ii]
Imam An Nawawi (R) stated:
That ordinary talk is forbidden in prayer, whether it relates to prayer or not. It is also forbidden to reply to a greeting of salaam verbally, but a response by gesture is allowed and desirable. All this is agreed upon by shafi and the majority of scholars. Abu Haneefah (R) said: He may not reply to the greeting either verbally or by signal in any case.’’[iii]
References:
[i] Nur-Al Idah, The light of clarification, Hasan Shurunbulali, Page 179, Al-Hidayah THE GUIDANCE, Burhan Al Din Al Farghani Al Marghinani, Vol 1 page 155
[ii] Muslim 540
[iii] Sharh al Muslim vol 4 page 241