Musnad Ahmad 31:409

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Abu Bishr, from Abu al-Mutawakkil, from Abu Sa'id al-Khudri, that some people from the companions of the Prophet (peace be upon him) came upon a tribe from the Arab tribes, but they did not host them. While they were in that state, the leader of those [people] was stung. They said, "Is there any medicine or a reciter among you?" They said, "You did not host us, and we will not do [anything] until you set a fee for us." So they set for them a herd of sheep. He said: He began to recite the Mother of the Quran (Al-Fatiha), gather his saliva, and spit. The man recovered. They brought them the sheep, but they said, "We will not take them until we ask the Messenger of Allah (peace be upon him) about that." They asked the Prophet (peace be upon him) about that, and he laughed and said, "What made you know that it is a Ruqyah (incantation)? Take them, and assign a share for me in it."