Mishkat al-Masabih #662

Abu Huraira reported God’s Messenger as saying, “When one of you gets up for prayer he must not spit in front, of him, because he is holding intimate converse with God as long as he is in his place of prayer; nor must he spit towards his right, for there is an angel at his right; but he may spit towards his left or under his feet and bury it.” The version of Abu Sa'id has “under his left foot.” (Bukhari and Muslim.)