‏الصلاة : Hadeeth No:1118 Abu Sa'id al-Khudri reported: The Prophet of Allaah (sallAllaahu alayhi wa sallam) saw sputum sticking to the Qibla of the mosque. He scratched it off with a pebble and then forbade spitting on the right side or in front, but (it is permissible) to spit on the left side or under the left foot....

‏التفسير : Hadeeth No:7188 This hadith has been transmitted on the same authority but with a slight variation of wording....