"I passed by Messenger of Allah (S) while he was performing Salat, so I said greeted him with Salam, and he returned it by making signals." He said: "I do not know except that he said: 'He indicated with his finger.'"  

مَرَرْتُ بِرَسُولِ اللَّهِ ﷺ وَهُوَ يُصَلِّي فَسَلَّمْتُ عَلَيْهِ فَرَدَّ إِلَىَّ إِشَارَةً وَقَالَ لاَ أَعْلَمُ إِلاَّ أَنَّهُ قَالَ إِشَارَةً بِإِصْبَعِهِ قَالَ وَفِي الْبَابِ عَنْ بِلاَلٍ وَأَبِي هُرَيْرَةَ وَأَنَسٍ وَعَائِشَةَ  

"I said to Bilal: 'How did the Prophet (S) reply to them when they gave him Salams and he was performing Salat?' He said: 'He would motion with his hand.'"  

قُلْتُ لِبِلاَلٍ كَيْفَ كَانَ النَّبِيُّ ﷺ يَرُدُّ عَلَيْهِمْ حِينَ كَانُوا يُسَلِّمُونَ عَلَيْهِ وَهُوَ فِي الصَّلاَةِ قَالَ كَانَ يُشِيرُ بِيَدِهِ