The Book of Mosques and Places of Prayer
وَحَدَّثَنِي يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا يَزِيدُ بْنُ زُرَيْعٍ، عَنِ الْجُرَيْرِيِّ، عَنْ أَبِي الْعَلاَءِ، يَزِيدَ بْنِ عَبْدِ اللَّهِ بْنِ الشِّخِّيرِ عَنْ أَبِيهِ، أَنَّهُ صَلَّى مَعَ النَّبِيِّ صلى الله عليه وسلم قَالَ فَتَنَخَّعَ فَدَلَكَهَا بِنَعْلِهِ الْيُسْرَى .Abdullah b. Shakhkhir narrated it on the authority of his father that he said prayer with the Messenger of Allah (ﷺ), and he spat and then rubbed it off with his left shoe
From Sahih Muslim, whose reports the scholars accept as authentic.