Jabir reported:The Messenger of Allah (ﷺ) sent me on an errand. I (having done the business assigned to me came back and) joined him as he was going (on a ride). Qutaiba said that he was saying prayer while he rode. I greeted him. He gestured to me. When he completed the prayer. he called me and said: You greeted me just now while I was engaged in prayer. (Qutaiba said): His (Prophet's face) was towards the east, as he was praying.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا لَيْثٌ، ح وَحَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَخْبَرَنَا اللَّيْثُ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، أَنَّهُ قَالَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم بَعَثَنِي لِحَاجَةٍ ثُمَّ أَدْرَكْتُهُ وَهُوَ يَسِيرُ - قَالَ قُتَيْبَةُ يُصَلِّي - فَسَلَّمْتُ عَلَيْهِ فَأَشَارَ إِلَىَّ فَلَمَّا فَرَغَ دَعَانِي فَقَالَ " إِنَّكَ سَلَّمْتَ آنِفًا وَأَنَا أُصَلِّي " . وَهُوَ مُوَجِّهٌ حِينَئِذٍ قِبَلَ الْمَشْرِقِ .
Muslim
The Book of Mosques and Places of Prayer • Hadith 45