Sahih Bukhari
Sahih Bukhari Volume 001, Book 008, Hadith Number 400.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 08. Prayers (Salat)
Narated By 'Abdullah bin 'Umar : Allah's Apostle saw sputum on the wall of the mosque in the direction of the Qibla and scraped it off. He faced the people and said, "Whenever any one of you is praying, he should not spit in front of him because in the prayer Allah is in front of him."