Musnad Ahmad 26:806

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim, from Al-Aswad, from Abdullah, who said: We were with the Prophet, peace and blessings of Allah be upon him, in a cave, and "Al-Mursalat 'Urfa" (Those sent forth in succession) was revealed to him. He said: We were taking it from his mouth while it was fresh, when a snake came out upon us. He said: "Kill it." He said: We rushed to kill it, but it escaped us. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Allah protected it from your evil, just as He protected you from its evil."