The Messenger of Allah ﷺ said, "Bilal, tell me about the deed you have done in Islam that you hope brings you the greatest reward, for last night I heard the soft sound of your sandals ahead of me in Paradise."Bilal replied, "I have done no deed in Islam that I hope brings me a greater reward than this, that whenever I perform a complete ablution at any hour of the night or day, I pray with that ablution as much as Allah has decreed for me to pray."
حدثنا ابن نمير قال حدثنا أبو حيان عن أبي زرعة
قال رسول الله ﷺ يا بلال حدثني بأرجى عمل عملته في الإسلام عندك منفعة فإني سمعت الليلة خشف نعليك بين يدي في الجنة فقال بلال ما عملت عملا في الإسلام أرجى عندي منفعة إلا أني لم أتطهر طهورا تاما في ساعة من ليل أو نهار إلا صليت بذلك الطهور ما كتب الله لي أن أصلي
Its isnad is sahih. Bukhari reported it, 2/67, in tahajjud, the virtue of purification by night and day, and Muslim, 4/1910, no. 2458, in the virtues of the companions, the virtues of Bilal, and Tirmidhi, 5/620, no. 3689, and he said, sahih gharib, and Hakim, 3/285.His saying "the sound of the sandals" means the noise of their tapping.