when a person uses siwak and then stands for night prayer an angel comes and stands behind him. the angel listens to the quranic recitation and slowly moves closer. He continues to listen and move closer until he finally places his mouth against the mouth of the person. Every ayah the person recites therafter would go into the angel. Thus clean your mouth when reciting quran ....recorded by al Bayhaqee, al Bazzaar, and others. varified to be authentic by al albani 9as saheehah no.1213 and saheeh ut Targheeb no,215)