Ibn 'Umar (may Allaah be pleased with him) narrated: “The Messenger
of Allaah (sallallaahu alayhi wa sallam) went to Qubaa’ to pray. Then the Ansaar
came to him and said salaam to him while he was praying. He said, ‘So, I said
to Bilaal, ‘How did you see the Messenger of Allah (sallallaahu alayhi wa
sallam)) reply to them when they said salaam to him while he was praying?’ He
said: ‘He replied like this.’ And he flattened his hand. Ja’far bin Awn (one of
the narrators) flattened his hand and made the bottom of the hand facing down
and the back of the hand facing up.” Saheeh, as-Saheehah, no. 185
Point of Benefit: After stating that the above mentioned hadeeth indicates that it
is recommended to say salaam to the one who is praying and to reply by means of
a gesture, Shaykh al-Albaanee (may Allaah have mercy on him) said: “Also
included among that is to say salaam to the one who is pronouncing the Adhaan
or reciting the Qur’aan, for it is legislated. The proof is what has preceded
(that is, the aforementioned hadeeth). This is because, if the recommendation
of saying salaam to the one who is praying is established, then saying salaam
to the one who is pronouncing the Adhaan or reciting the Qur’an is more
deserving and more proper...
Should both of them reply the salaam verbally or with a gesture? The
first is what is apparent.[1] Imam an-Nawawee said: ‘As for the
Mu’adhdhin, it is not disliked for him to respond with the usual utterance
because that is easy and it will neither invalidate the Adhaan nor make it
defective.
Source: Nudhum al-Faraa’id mimma fee Silsilati al-Albaanee min Fawaa’id, vol. 2, p. 222 by Abdul-Lateef bin Muhammad bin Ahmad bin Abee Rabee’
