(36) باب لِيَبْزُقْ عَنْ يَسَارِهِ، أَوْ تَحْتَ قَدَمِهِ الْيُسْرَى
Narrated Abu Sa`id:
The Prophet (ﷺ) saw sputum on (the wall of) the mosque in the direction of the Qibla and scraped it off with gravel. Then he forbade Spitting in front or on the right, but allowed it on one's left or under one's left foot.
Reference: Sahih al-Bukhari 414
In-book reference: Book 8, Hadith 64
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 8, Hadith 406