'Aishah (May Allah be pleased with her) said:
The Messenger of Allah (ﷺ) saw spittle or snot or sputum, sticking to the wall towards Qiblah and scratched it off.[Al-Bukhari and Muslim]. (IT)
App reference (IT): Book 18, Hadith 184 (IT)
Arabic/English book reference (IT): Book 18, Hadith 1694 (IT)