Musannaf Ibn Abi Shayba 3:2592

Mu'tamir narrated to us, from Bard, from Sulayman ibn Musa, who said: The Prophet of Allah, peace and blessings of Allah be upon him, saw a man praying while sitting. The Prophet, peace and blessings of Allah be upon him, said: "Why are you praying while sitting?" He said: "A scorpion stung me." He said: "If one of you sees a scorpion, even if he is in prayer, let him take his left sandal and kill it with it."