SPITTING. According to the Traditions, Muslims must spit on the left side, and cover it over with earth. Spitting in mosques is forbidden. (See ‘Abdu ‘l-Haqq’s Comnentary on the Miskat, vol. i. p. 295.) Muhammad said: “Spit not in front, for you are in God’s presence. Spit not on the right hand, for there standeth the angel who recordeth your good actions.”
Based on Hughes, Dictionary of Islam