Hadith 1186

It was narrated that Suhaib, the Companion of the Messenger of Allah (SAW) said: "I passed by the Messenger of Allah (SAW) when he was praying, and greeted him with Salam. He returned my greeting with a gesture, or maybe it was just with his finger."

أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ بُكَيْرٍ، عَنْ نَابِلٍ، صَاحِبِ الْعَبَاءِ عَنِ ابْنِ عُمَرَ، عَنْ صُهَيْبٍ، صَاحِبِ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ مَرَرْتُ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم وَهُوَ يُصَلِّي فَسَلَّمْتُ عَلَيْهِ فَرَدَّ عَلَىَّ إِشَارَةً وَلاَ أَعْلَمُ إِلاَّ أَنَّهُ قَالَ بِإِصْبَعِهِ ‏.‏

Reference: 1111910
In-book reference: Book 13, Hadith 1186
Hadith 1186 - The Book of Forgetfulness (In Prayer) - Sunan an-Nasa'i - Sunnah.com