The Apostle of Allaah ( sal Allaahu alayhi wa sallam ) entered a park. He was accompanied by a boy who had a jug of water with him. He was the youngest of us. He placed it near the lote-tree. He ( the Prophet, sal Allaahu alayhi wa sallam ) relieved himself. He came to us after he had cleansed himself with water.  

أَنَّ رَسُولَ اللَّهِ ﷺ دَخَلَ حَائِطًا وَمَعَهُ غُلاَمٌ مَعَهُ مِيضَأَةٌ وَهُوَ أَصْغَرُنَا فَوَضَعَهَا عِنْدَ السِّدْرَةِ فَقَضَى حَاجَتَهُ فَخَرَجَ عَلَيْنَا وَقَدِ اسْتَنْجَى بِالْمَاءِ  

The Prophet ﷺ said: The following verse was revealed in connection with the people of Quba': "In it are men who love to be purified" (ix.108). He (AbuHurayrah) said: They used to cleanse themselves with water after easing. So the verse was revealed in connection with them.  

عَنِ النَّبِيِّ ﷺ قَالَ نَزَلَتْ هَذِهِ الآيَةُ فِي أَهْلِ قُبَاءَ { فِيهِ رِجَالٌ يُحِبُّونَ أَنْ يَتَطَهَّرُوا } قَالَ كَانُوا يَسْتَنْجُونَ بِالْمَاءِ فَنَزَلَتْ فِيهِمْ هَذِهِ الآيَةُ