Musannaf Ibn Abi Shayba 1:1799

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from al-A'mash, from Sa'd ibn 'Ubaydah, from Abu 'Abd al-Rahman, from 'Ali, who said: "When one of you rises at night, let him use the tooth stick (siwak), for when a man rises at night and uses the tooth stick, then performs ablution, then stands for prayer, an angel comes to him and stands behind him, listening to the Qur'an. He continues to draw near to him until he places his mouth upon his mouth, so that he does not recite a verse except that it enters his interior."