Musnad Ahmad 26:513

Hajjaj narrated to us, Sufyan narrated to us, Mansur narrated to us, from Ibrahim, from Alqama, from Ibn Mas’ud, who said: We were with the Messenger of Allah, peace and blessings of Allah be upon him, in a cave, when "By the winds sent forth in gusts" (Al-Mursalat) was revealed to him. We were receiving it from him, when a snake emerged from the side of the cave. He said: "Kill it." We rushed toward it, but it escaped us. He said: "It was protected from your evil, just as you were protected from its evil."