Yahya related to me from Malik from Hisham ibn Urwa from his
father from A'isha, the wife of the Prophet, mayAllah bless him and
grant him peace, that the Prophet, may Allah bless him and grant him
peace, saw spittle, or mucus or phlegm, on the wall of the qibla and
scraped it off.
Muwatta Malik Book 14, Hadith 6