The Second Section: The Salam by the Tongue or by Gesture.

The Shaykh : The Second Section: Does one give the Salam by gesture or by speech and with the tongue?
Answer: The second option, which is speaking it with the tongue. Giving the Salam by gesture is prohibited, except in two cases: if a person is far away and one fears that the one being greeted will not hear, then he gestures with his hand along with the words, "As-salamu alaykum."
The second case: if a person is praying, then if a Muslim greets him, he does not respond with his tongue, but rather responds with a gesture, raising his hand like this, whether he is standing and saying this, or sitting and saying this, indicating that he is praying and that he is unable to respond.
We add a third case: if a person is listening to the Friday sermon and a Muslim greets him, he does not return the Salam, because speaking during the Friday sermon is forbidden, except for the preacher and the one the preacher addresses out of need or benefit. So if a person prays next to you, for example, while the imam is delivering the sermon, and he entered the mosque while the imam was preaching, and he prayed the greeting of the mosque and greeted you, do not return the Salam. However, it is recommended that you gesture to him that there is no response. And when the sermon ends, return the Salam to him and explain to him that the sermon is not a place for Salam. Do you understand? Good.
Likewise, we add a fourth case: if a person is relieving himself—meaning in the bathroom—and a Muslim greets him, he does not return the Salam, because he has now exposed his 'awrah (nakedness). And he is in a place where it is not possible to respond. In fact, the Prophet (peace and blessings be upon him) was greeted by a man one day, and he was not in a state of wudu (ablution), so he performed tayammum (dry ablution) with the wall, then returned the Salam, and then said: . It is obligatory for one who greets a group of people in which there are Muslims and disbelievers to intend the Salam for whom? For the Muslims only. If one greets a group in a gathering where some are sleeping and some are awake, for whom does he give the Salam? For the awake ones, and he lowers his voice so as not to wake the sleepers, because this is from the Sunnah (recommended practice) not to raise one's voice near sleepers, because one might wake them. And some people, when they wake up after sleeping, do not sleep again. They remain anxious, tossing and turning in their beds, and the night becomes long for them. So whenever it is possible to lower your voice, that is what is required, so as not to wake the sleepers.