Musnad Ahmad 30:699

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Yahya ibn Abi Kathir—I think he said: from Damdam, from Abu Hurayrah, who said: "The Messenger of Allah, may Allah bless him and grant him peace, commanded us to kill the two black ones during prayer: the scorpion and the snake." And 'Abd al-Razzaq said: "This is how he narrated it to us, more times than I can count."