Prayer: Making the Reply to Salaam Heard
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1125
One must reply to salaam in a manner that the person who said salaam to him hears the reply. However, if the person who said salaam is deaf or passes by quickly having said salaam, in the event that it is possible to make that person aware of the reply by indicating and suchlike, it is necessary to do so. In other cases – except during prayers – it is not necessary to reply, and during prayers it is not permitted.