The Messenger of Allah ﷺ went out to Quba to pray there. The Ansar came and greeted him while he was praying.I asked Bilal, "How did you see the Messenger of Allah ﷺ respond to them when they greeted him while he was praying?"He replied, "He would do like this," and he stretched out his palm. Jafar bin Awn stretched out his palm, placing the inside of it facing downward and the back of it facing upward.
حدثنا الحسين بن عيسى الخراساني الدامغاني حدثنا جعفر بن عون حدثنا هشام بن سعد حدثنا نافع قال سمعت
خرج رسول الله ﷺ إلى قباء يصلي فيه قال فجاءته الأنصار فسلموا عليه وهو يصلي قال فقلت لبلال كيف رأيت رسول الله ﷺ يرد عليهم حين كانوا يسلمون عليه وهو يصلي قال يقول هكذا وبسط كفه وبسط جعفر بن عون كفه وجعل بطنه أسفل وجعل ظهره إلى فوق
[Sahih] Recorded by Tirmidhi in the Book of Prayer, chapter on what has been said about gesturing during prayer, no. 368, from the hadith of Hisham bin Saad, and he said, hasan sahih. Ibn Jarud also graded it sahih, no. 215, and the hadith has corroborating narrations.