Sahih Bukhari
Sahih Bukhari Volume 001, Book 008, Hadith Number 401.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 08. Prayers (Salat)
Narated By 'Aisha : (The mother of faithful believers) Allah's Apostle saw some nasal secretions, expectoration or sputum on the wall of the mosque in the direction of the Qibla and scraped it off.