Hadith 1115:4
Waki’ narrated to us, Hisham bin Sa’d narrated to us, from Nafi’, from Ibn Umar, who said: I said to Bilal, "How did the Prophet, peace and blessings of Allah be upon him, respond to them when they would greet him while he was in prayer?" He said: "He would gesture with his hand."
حدثنا وكيع، حدثنا هشام بن سعد، عن نافع، عن ابن عمر، قال: قلت لبلال كيف كان النبي صلى الله عليه وسلم يرد عليهم حين كانوا يسلمون عليه في الصلاة؟ قال: " كان يشير بيده "