The Book of the Masjids
8/34. Chapter:
With Which Foot Should He Rub (His Spittle)?
Sunan an-Nasai
أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ سَعِيدٍ الْجُرَيْرِيِّ، عَنْ أَبِي الْعَلاَءِ بْنِ الشِّخِّيرِ، عَنْ أَبِيهِ، قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم تَنَخَّعَ فَدَلَكَهُ بِرِجْلِهِ الْيُسْرَى .
It was narrated from Abu Al-'Ala' bin Ash-Shikhir that his father said: "I saw the Messenger of Allah (ﷺ) spit and then rub it with his left foot."
Reference : Sunan an-Nasa'i 727In-book reference : Book 8, Hadith 40English translation : Vol. 1, Book 8, Hadith 728