Musnad Ahmad 3723

It was narrated that Abul Ahwas al-Jushami said: Whilst Ibn Mas’ood was delivering a khutbah one day, he saw a snake on the wall, so he interrupted his khutbah and struck it with his stick or cane and killed it, then he said: I heard the Messenger of Allah (ﷺ) say: "Whoever kills a snake, it is as if he killed a mushrik man whose blood it is permissible to shed.”