Sahih al-Bukhari, Hadith 407 ⓘ
Narrated `Aisha: (the mother of faithful believers) Allah's Messenger saw some nasal secretions, expectoration or sputum on the wall of the mosque in the direction of the Qibla and scraped it off.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ أُمِّ الْمُؤْمِنِينَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَأَى فِي جِدَارِ الْقِبْلَةِ مُخَاطًا أَوْ بُصَاقًا أَوْ نُخَامَةً فَحَكَّهُ.
also referenced under: Book 8, Hadith 59 (In-Book) & Volume 1, Book 8, Hadith 401 (USC-MSA)