A man came to the Prophet; he had performed ablution and has missed a spot the size of a fingernail where water had not reached. The Prophet said to him: 'Go back and perform ablution properly.'"
أَنَّ رَجُلاً أَتَى النَّبِيَّ ﷺ وَقَدْ تَوَضَّأَ وَتَرَكَ مَوْضِعَ الظُّفْرِ لَمْ يُصِبْهُ الْمَاءُ فَقَالَ لَهُ النَّبِيُّ ﷺ ارْجِعْ فَأَحْسِنْ وُضُوءَكَ