Musnad Ahmad 26:518

Aswad ibn Amir narrated to us, Isra'il narrated to us, from al-A'mash and Mansur, from Ibrahim, from Alqama, from Abdullah, who said: We were with the Messenger of Allah, peace and blessings of Allah be upon him, in the cave, when a snake came out toward us. We rushed toward it, but it beat us to it and entered the hole. The Prophet, peace and blessings of Allah be upon him, said: "It was protected from your evil, just as you were protected from its evil." He said: And al-A'mash added in the hadith, he said: We were receiving it from his mouth while it was moist.