Reference: http://www.alfawzan.af.org.sa/node/15964
Question: If a Muslim extends the [greeting of] salaam [‘alaykum] to his [Muslim] brother with a sign [with his hand] – whilst moving his lips, should the response [to him] be with the right or left hand if he is at a distance?
Response: Yes, he should respond to him by raising his hand to let him know he is extending the [greeting of] salaam to him; meaning, he should not suffice with just a sign [with his hand], rather he should raise his hand and extend the [greeting of] salaam to him, and the other [person] should return [the greeting] with the same.
