It is narrated from Nafi that Abdullah bin Umar, may Allah be pleased with them both, passed by a man who was praying, so he greeted him with salam. The man replied with his tongue. Then Abdullah bin Umar, may Allah be pleased with them both, returned and said to him: When someone greets you with salam while you are praying, do not reply with your tongue, but rather respond by gesturing with your hand.