Sahih Bukhari
Sahih Bukhari Volume 002, Book 022, Hadith Number 305.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 22. Actions While Praying
Narated By Anas : The Prophet said, "Whenever anyone of you is in prayer, he is speaking in private to his Lord and so he should neither spit in front of him nor on his right side but to his left side under his left foot."