Sunan an-Nasa'i
Book 8: The Book of the Masjids
كتاب المساجد
54 hadith in this book
Chapter 34 With Which Foot Should He Rub (His Spittle)?
باب بِأَىِّ الرِّجْلَيْنِ يَدْلُكُ بُصَاقَهُ
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."
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 .
Hadith text, translations and grading are courtesy of Sunnah.com.