Musannaf Ibn Abi Shayba 3:5074

Hafs narrated to us, from Humayd, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) saw phlegm in the mosque, so he wiped it away. Then he said: "If one of you spits, let him not spit towards the Qibla, nor to his right, but let him spit to his left or under his foot." Or he said: "Let him place [it] or spit like this." Then he spat into the edge of his garment, then folded it over.