"I passed by the Messenger of Allah ﷺ when he was praying, and greeted him with Salam. He returned my greeting with a gesture, or maybe it was just with his finger." (Using translation from Nasāʾī 1186)  

عَنْ صُهَيْبٍ صَاحِبَ رَسُولِ اللهِ ﷺ قَالَ «مَرَرْتُ عَلَى رَسُولِ اللهِ ﷺ وَهُوَ يُصَلِّي فَسَلَّمْتُ عَلَيْهِ فَرَدَّ عَلَيَّ إِشَارَةً وَلَا أَعْلَمُ إِلَّا أَنَّهُ قَالَ بِإصْبُعِهِ»  

"Ibn 'Umar said: The Prophet ﷺ entered the Masjid of Quba' to pray there, then some men came in and greeted him with Salam. I asked Suhaib, who was with him: 'What did the Messenger of Allah ﷺ do when he was greeted?' He said: 'He used to gesture with his hand.'" (Using translation from Nasāʾī 1187)  

قَالَ ابْنُ عُمَرَ دَخَلَ النَّبِيُّ ﷺ مَسْجِدَ قُبَاءٍ لَيُصَلِّي فِيهِ فَدَخَلَ عَلَيْهِ رِجَالٌ يُسَلِّمُونَ عَلَيْهِ فَسَأَلْتُ صُهَيْبًا وَكَانَ مَعَهُ كَيْفَ كَانَ النَّبِيُّ ﷺ يَصْنَعُ إِذَا سَلَّمَ عَلَيْهِ؟ قَالَ كَانَ يُشِيرُ بِيَدِهِ  

He greeted the Messenger of Allah ﷺ with the Salam when he was praying, and he returned the greeting. (Using translation from Nasāʾī 1188)  

أَنَّهُ «سَلَّمَ عَلَى رَسُولِ اللهِ ﷺ وَهُوَ يُصَلِّي فَرَدَّ عَلَيْهِ»  

"The Messenger of Allah ﷺ sent me on an errand then I came back to him while he was praying. I greeted him with the salam and he gestured to me. When he finished he called me and said: 'You greeted me with Salam just now and I was praying.' And he was facing toward the east that day." (Using translation from Nasāʾī 1189)  

بَعَثَنِي رَسُولُ اللهِ ﷺ لِحَاجَةٍ ثُمَّ أَدْرَكْتُهُ وَهُوَ يُصَلِّي فَسَلَّمْتُ عَلَيْهِ فَأَشَارَ إِلَيَّ فَلَمَّا فَرَغَ دَعَانِي فَقَالَ «إِنَّكَ سَلَّمْتَ عَلَيَّ آنِفًا وَأَنَا أُصَلِّي إِنَّمَا هُوَ مُوَجِّهٌ حِينَئِذٍ إِلَى الْمَشْرِقِ»  

"The Messenger of Allah ﷺ sent me on an errand, then I came back to him while he was facing the east or the west. I greeted him with salam and he gestured to me. Then when he finished he called me and said: "O Jabir!" So I came and said: "O Messenger of Allah, I greeted you with Salam but you did not answer." He said: 'I was praying.' (Using translation from Nasāʾī 1190)   

بَعَثَنِي النَّبِيُّ ﷺ فَأَتَيْتُهُ وَهُوَ يَسِيرُ مُشَرِّقًا أَوْ مُغَرِّبًا فَسَلَّمْتُ عَلَيْهِ فَأَشَارَ بِيَدِهِ ثُمَّ سَلَّمْتُ فَأَشَارَ بِيَدِهِ فَانْصَرَفْتُ فَنَادَانِي النَّاسُ يَا جَابِرُ فَأَتَيْتُهُ فَقُلْتُ يَا رَسُولَ اللهِ إِنِّي سَلَّمْتُ عَلَيْكَ فَلَمْ تَرُدَّ عَلَيَّ فَقَالَ «إِنِّي كُنْتُ أُصَلِّي» قَالَ أَبُو عَبْدِ الرَّحْمَنِ زَعَمُوا أَنَّهُ لَيْسَ هَذَا الْحَدِيثُ بِمِصْرَ مِنْ حَدِيثِ عَمْرِو بْنِ الْحَارِثِ