The Prophet ﷺ said to Bilal at the time of the Fajr prayer, "Bilal, tell me about the deed you have done in Islam that you hope for the most, for I heard the sound of your sandals ahead of me in Paradise."Bilal replied, "I have done no deed that I place greater hope in than this, that I never perform ablution at any hour of the night or day without praying with that ablution whatever has been decreed for me to pray."
أن النبي ﷺ قال لبلال عند صلاة الفجر: يا بلال! حدثني بأرجى عمل عملته في الإسلام، فاني سمعت دف نعليك بين يدي في الجنة قال: ما عملت عملا أرجى عندي، أني لم أتطهر طهورا في ساعة ليل أو نهار إلا صليت بذلك الطهور ما كتب لي أن أصلي.
Bukhari related it in the book of tahajjud (1149) and Muslim in the book of the virtues of the companions (2458), both from the hadith of Abu Usama, from Abu Hayan, from Abu Zura, from Abu Hurairah, who mentioned it similarly, and the wording given is that of Bukhari. In Muslim's wording it reads, "O Bilal, tell me about the most hopeful deed you have done in Islam in terms of benefit, for I heard tonight the sound of your sandals in front of me in Paradise."