Sunan at-Tirmidhi (Jami-al-Tirmidhi), Chapter: Salah (Prayers)

that Walid ibn Hisham al-Mu'ayti reported to him that Ma'dan ibn Talhah al-Ya'muri narrated to him that he met Sayyidina Thawban (RA) (the freedman of Allah's Messenger (SAW)) He asked him, "Guide me to a deed that should benefit me in the sight of Allah and he may admit me to Paradise." He thought over a moment, then turning to him said. "You should make (plenty of) prostrations for. I have heard Allah's Messenger (SAW) say, "No slave of Allah prostrates before Allah but he raises him a degree and erases from him a sin."