Musannaf Ibn Abi Shayba 3:5627

Hafs narrated to us, from Dawud, from Shahr ibn Hawshab, who said: "Indeed, the Shaytan comes to one of you and inserts his finger into his anus, then he moves it and moves his private part so that it becomes erect. So, he must not depart until he hears a sound or smells an odor."