Abdullah bin Umar (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) entered the mosque of Banu Amr bin Awf to pray in it, and Suhayb (may Allah be pleased with him) entered with him (peace and blessings be upon him). Then some men of the Ansar came to greet him (peace and blessings be upon him) with salam. Abdullah (may Allah be pleased with him) said: So I asked Suhayb (may Allah be pleased with him) what the Messenger of Allah (peace and blessings be upon him) used to do when he was greeted with salam during the prayer. He said: He (peace and blessings be upon him) used to gesture with his hand.
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7260