It was narrated that Jabir said:

"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.'

أَخْبَرَنَا مُحَمَّدُ بْنُ هَاشِمٍ الْبَعْلَبَكِّيُّ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ شُعَيْبِ بْنِ شَابُورٍ، عَنْ عَمْرِو بْنِ الْحَارِثِ، قَالَ أَخْبَرَنِي أَبُو الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ بَعَثَنِي النَّبِيُّ ﷺ فَأَتَيْتُهُ وَهُوَ يَسِيرُ مُشَرِّقًا أَوْ مُغَرِّبًا فَسَلَّمْتُ عَلَيْهِ فَأَشَارَ بِيَدِهِ ثُمَّ سَلَّمْتُ عَلَيْهِ فَأَشَارَ بِيَدِهِ فَانْصَرَفْتُ فَنَادَانِي " يَا جَابِرُ " . فَنَادَانِي النَّاسُ يَا جَابِرُ . فَأَتَيْتُهُ فَقُلْتُ يَا رَسُولَ اللَّهِ إِنِّي سَلَّمْتُ عَلَيْكَ فَلَمْ تَرُدَّ عَلَىَّ . فَقَالَ " إِنِّي كُنْتُ أُصَلِّي " .