Sahih Bukhari | Volume 1 | Hadith Number 508

Narrated by Anas
The Prophet said, "Whenever anyone of you offers his prayer he is speaking in private to his Lord. So he should not spit to his right but under his left foot." Qatada said, "He should not spit in front of him but to his left or under his feet." And Shu'ba said, "He should not spit in front of him, nor to his right but to his left or under his foot." Anas said: The Prophet said, "He should neither spit in the direction of his Qibla nor to his right but to his left or under his foot."