The Messenger of Allah (ﷺ) went to Quba to offer prayer. Then the Ansar (the Helpers) came to him and gave him a salutation while he was engaged in prayer.

I asked Bilal: How did you find the Messenger of Allah (ﷺ) responding to them when they gave him a salutation while he was engaged in prayer. He replied: In this way, and Ja'far ibn Awn demonstrated by spreading his palm, and keeping its inner side below and its back side above.
Sunan Abi Dawud Book 2, Hadith 538
← Previous Hadith The prophet of Allah(ﷺ) sent me to Banu al-Mustaliq. When I returned to him, he was praying on his camel. I talked to him; he made a sign to me with his hand like this. I again talked to him; he made a sign to me with his hand like this. I was hearing him reciting the Qur’an and he was making a sign with his head. When he finished his prayer, he said; what did you do about the mission for which I had sent you; nothing prevented me from talking to you except that I was praying.

Sunan Abi Dawud Book 2, Hadith 537 Next Hadith → There is no loss in prayer nor in salutation. Ahmad(b. Hanbal) said: This means, I think, that you do not salute nor you are saluted by others. The loss of a man in his prayer is that a man remains doubtful about it when he finishes it.

Sunan Abi Dawud Book 2, Hadith 539