Silsilat al-Ahadith al-Sahihah

Sayyiduna Tariq bin Abdullah (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him), he said: "When you pray, do not spit in front of you nor to your right side, but if there is space on your left side then spit there, otherwise spit beneath your feet and rub it in."

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When any one of you stands for prayer, he should not spit in front of him because when he is in prayer, he is whispering to his Lord. Nor should he spit to his right, for there is an angel on his right. (However,) he may spit to his left or spit under his foot and bury it."

It is narrated from Sayyiduna Hudhaifah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When a person stands in prayer, Allah Almighty turns towards him with His Face. Therefore, the one praying should not spit in front of him, nor to his right side, because the angel who records good deeds is on his right side. (However), he should spit to his left side."