How does the one who is praying return the salam to the one who greeted him?

The Shaykh : They respond to him with a gesture, saying, “As-salamu alaykum” (peace be upon you) in this manner. You do not say “As-salamu alaykum” with your tongue, but only with a gesture. If he remains until you have finished your prayer, they respond to him with words. If he leaves, the gesture is sufficient. But do you greet the one who is praying or not? You look at the one who is praying. The one praying may be an ordinary person; if you greet him and say “As-salamu alaykum,” he responds with words and says, “And upon you, peace.” In that case, I might say—perhaps, I might say—he would abandon the prayer, and it is not preferable if he is ignorant. But if he is a student of knowledge, he does not accept words; if you greet him, he accepts the gesture, as he was commanded to do. And for the married man…