Abu Huraira reported that God's Messenger said to Bilal at the dawn prayer, “Tell me, Bilal, of the action you have done since becoming a Muslim which is most calculated to cause hope in you, for I heard the sound of your sandals in front of me in paradise.” He replied, “I have done no action more calculated, in my opinion to cause hope than that I have never performed ablution at any hour of the night or day without immediately praying what was ordained for me to pray.”
(Bukhari and Muslim.)