Umar ibn al-Khattab reported: A man performed ablution and he left out a spot on his foot the size of a fingernail. The Prophet, peace and blessings be upon him, said, “Go back and perform ablution well.” The man went back and then prayed.
Source: Ṣaḥīḥ Muslim 243
Grade: Sahih (authentic) according to Muslim
Al-Nawawi said, “Al-Qadi ‘Iyad and others used this tradition as evidence for the obligation of continuity in ablution.”
Source: Sharḥ al-Nawawī ‘alá Ṣaḥīḥ Muslim 242
عن عمر بن الخطاب أَنَّ رَجُلًا تَوَضَّأَ فَتَرَكَ مَوْضِعَ ظُفُرٍ عَلَى قَدَمِهِ فَأَبْصَرَهُ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ ارْجِعْ فَأَحْسِنْ وُضُوءَكَ فَرَجَعَ ثُمَّ صَلَّى
243 صحيح مسلم كتاب الطهارة باب وجوب استيعاب جميع أجزاء محل الطهارة
قال النووي وَاسْتَدَلَّ الْقَاضِي عِيَاضٌ وَغَيْرُهُ بِهَذَا الْحَدِيثِ عَلَى وُجُوبِ الْمُوَالَاةِ فِي الْوُضُوءِ
242 شرح النووي على مسلم