Musnad Ahmad 75:2

Yahya ibn Sa'id narrated to us, from Shu'bah, from Simak, who said: Muhammad ibn Hatib said: "Some [boiling] liquid from a pot spilled onto my hand, so my mother took me to the Messenger of Allah, may Allah bless him and grant him peace, while he was in a certain place." He said: "He spoke words, among which were: 'Remove the harm, O Lord of the people'—and I think he said—'Heal, for You are the Healer.'" He said: "And he was spitting [lightly, without saliva]."