It was narrated that Abu Umamah said, in a marfu' Hadith:
"Adhere to righteousness and it is a blessing if you are able to do so. Know that the best of your deeds is prayer and that no one maintains his ablution except a believer." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 279 (RU)
Arabic reference (RU): Book 1, Hadith 292 (RU)