Hadith: O Bilāl, tell me of the most rewarding deed you have done in Islam

عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ أَنَّ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ لِبِلاَلٍ عِنْدَ صَلاَةِ الفَجْرِ:
«يَا بِلاَلُ، حَدِّثْنِي بِأَرْجَى عَمَلٍ عَمِلْتَهُ فِي الإِسْلاَمِ، فَإِنِّي سَمِعْتُ دَفَّ نَعْلَيْكَ بَيْنَ يَدَيَّ فِي الجَنَّةِ» قَالَ: مَا عَمِلْتُ عَمَلًا أَرْجَى عِنْدِي أَنِّي لَمْ أَتَطَهَّرْ طَهُورًا، فِي سَاعَةِ لَيْلٍ أَوْ نَهَارٍ، إِلَّا صَلَّيْتُ بِذَلِكَ الطُّهُورِ مَا كُتِبَ لِي أَنْ أُصَلِّيَ.
[صحيح] - [متفق عليه] - [صحيح البخاري: 1149]

Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (ﷺ) said to Bilāl at the time of the Fajr prayer:
"O Bilāl, tell me of the most rewarding deed you have done in Islam, for verily I heard the scuffle of your sandals ahead of me in Paradise." He (Bilāl) said: I do not consider any deed I have done more rewarding except that I never made ablution at any time of night or day without praying with that ablution as much as was ordained for me to pray.
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 1149]

Explanation

The Prophet (ﷺ) saw in a dream that he was in Paradise. He said to Bilāl ibn Rabāh: Tell me about the most rewarding voluntary deed you have done in Islam, for I heard the soft sound of your sandals ahead of me in Paradise. Bilāl said: The deed I consider most rewarding is that whenever I break my ablution, I perform ablution—at any hour of the day or night— and I would pray with that ablution as many voluntary prayers as ordained for me to pray.

Benefits from the Hadith

1. The virtue of the deed indicated by Bilāl (may Allah be pleased with him)—namely, praying whenever one performs purification and ablution—and that it is among the most rewarding of deeds and a means of entering Paradise.
2. It is commendable to offer prayer after every ablution.
3. The example of a role model or mentor asking his student about his deeds—to encourage him to remain steadfast if they are good, or to advise him against them if they are not.
4. A testimony from the Prophet (ﷺ) that Bilāl (may Allah be pleased with him) is among the people of Paradise.
5. This question took place at the time of the Fajr prayer, indicating that it occurred in a vision seen by the Prophet (ﷺ)—and the visions of the prophets are true.