Hadith
حَدَّثَنَا الْحُسَيْنُ بْنُ عِيسَى الْخُرَاسَانِيُّ الدَّامَغَانِيُّ، حَدَّثَنَا جَعْفَرُ بْنُ عَوْنٍ، حَدَّثَنَا هِشَامُ بْنُ سَعْدٍ، حَدَّثَنَا نَافِعٌ، قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ عُمَرَ، يَقُولُ خَرَجَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِلَى قُبَاءَ يُصَلِّي فِيهِ - قَالَ - فَجَاءَتْهُ الأَنْصَارُ فَسَلَّمُوا عَلَيْهِ وَهُوَ يُصَلِّي . قَالَ فَقُلْتُ لِبِلاَلٍ كَيْفَ رَأَيْتَ رَسُولَ اللَّهِ صلى الله عليه وسلم يَرُدُّ عَلَيْهِمْ حِينَ كَانُوا يُسَلِّمُونَ عَلَيْهِ وَهُوَ يُصَلِّي قَالَ يَقُولُ هَكَذَا وَبَسَطَ كَفَّهُ . وَبَسَطَ جَعْفَرُ بْنُ عَوْنٍ كَفَّهُ وَجَعَلَ بَطْنَهُ أَسْفَلَ وَجَعَلَ ظَهْرَهُ إِلَى فَوْقٍ .
Narrated Abdullah ibn Umar: 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
Sahih · Al-Albani
Sunan Abi Dawud 927 ·Book 2, Hadith 538·Also available on sunnah.com·