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.
The chain is ordered from the source of the saying to the compiler: 1 = the speaker/first transmitter, the following links those who passed it on in turn, and at the bottom al-Bukhari who compiled the work. Click a narrator to list every hadith in which he appears; the number in parentheses is how many hadiths across the collections on this site the narrator appears in.