It is narrated from Sayyiduna Tariq bin Abdullah al-Yamani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When you spit, do not spit in front of you, nor to your right; rather, spit to your left if it is clear, or under your foot."
Hadith Referenceالمعجم الكبير للطبراني / باب الطاء / 8139