The Apostle of Allah ﷺ 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. (Using translation from Muslim 548a)
أَنَّ رَسُولَ اللهِ ﷺ رَأَى نُخَامَةً فِي قِبْلَةِ الْمَسْجِدِ فَحَكَّهَا بِيَدِهِ