Sahih Muslim Book - 5, Hadith - 1205

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ حَدَّثَنَا لَيْثٌ ح وَحَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ أَخْبَرَنَا اللَّيْثُ عَنْ أَبِى الزُّبَيْرِ عَنْ جَابِرٍ أَنَّهُ قَالَ إِنَّ رَسُولَ اللَّهِ -صلى الله عليه وسلم- بَعَثَنِى لِحَاجَةٍ ثُمَّ أَدْرَكْتُهُ وَهُوَ يَسِيرُ - قَالَ قُتَيْبَةُ يُصَلِّى - فَسَلَّمْتُ عَلَيْهِ فَأَشَارَ إِلَىَّ فَلَمَّا فَرَغَ دَعَانِى فَقَالَ « إِنَّكَ سَلَّمْتَ آنِفًا وَأَنَا أُصَلِّى ». وَهُوَ مُوَجِّهٌ حِينَئِذٍ قِبَلَ الْمَشْرِقِ.

It was narrated that Jabir bin 'Abdullah said: "The Messenger of Allah (s.a.w) sent me on an errand, then I caught up with him as he was setting out" - Qutaibah said: "when he was praying" - "I greeted him and he gestured to me. When he had finished he called me and said: 'You greeted me just now while I was praying.' And he was facing towards the east on that occasion.''