Hadith 504620
Chapter 14: The Qibla - كتاب القبلة
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ صلى
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.
Reference Muwatta Malik 504620
USC-MSA web (English) reference : Book 14, Hadith 5