The Apostle of Allah (may, peace be upon him) saw spittle or snot or sputum, sticking to the wall towards Qibla and scratched it off.
Sahih Muslim Book 5, Hadith 65
← Previous Hadith Abu Huraira and Abu Sa'id narrated that the Messenger of Allah (ﷺ) saw sputum, and the rest of the hadith is the same.

Sahih Muslim Book 5, Hadith 64 Next Hadith → How Is it that someone amongst you stands before his Lord and then spits out in front of Him? Does any one of you like that he should be made to stand in front of someone and then spit at his face? So when any one of you spits, he must spit on his left side under his foot. But if he does not find (space to spit) he should do like this. Qasim (one of the narrators) spat in his cloth and then folded it and rubbed it.

Sahih Muslim Book 5, Hadith 66