Musannaf Ibn Abi Shayba 21:681

'Abd al-Rahim ibn Sulayman narrated to us, from Mutarrif, from al-Minhal ibn 'Amr, from Muhammad ibn 'Ali, from 'Ali, who said: While the Messenger of Allah (may Allah bless him and grant him peace) was praying one night, he placed his hand on the ground, and a scorpion stung him. The Messenger of Allah (may Allah bless him and grant him peace) reached for it with his sandal and killed it. When he finished, he said: "May Allah disgrace the scorpion; it does not leave a person praying, nor anyone else, nor a believer, nor anyone else, without stinging them." Then he called for salt and water, placed them in a vessel, and began pouring it over his finger where it had stung him, wiping it and seeking refuge for it by reciting the two surahs of seeking refuge (al-Mu'awwidhatayn).