حَدَّثَنَا حَرْمَلَةُ بْنُ يَحْيَى، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ وَهْبٍ، حَدَّثَنَا جَرِيرُ بْنُ حَازِمٍ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، أَنَّ رَجُلاً، أَتَى النَّبِيَّ ـ صلى الله عليه وسلم ـ وَقَدْ تَوَضَّأَ وَتَرَكَ مَوْضِعَ الظُّفْرِ لَمْ يُصِبْهُ الْمَاءُ فَقَالَ لَهُ النَّبِيُّ ـ صلى الله عليه وسلم ـ ‏"‏ ارْجِعْ فَأَحْسِنْ وُضُوءَكَ ‏"‏ ‏.‏

It was narrated from Anas that: 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.'" Translation Not Available

Book Ref: Sunan Ibn Majah Book 1 Hadith 665
Web Ref:  Sunan Ibn Majah Vol 1 Book 1 Hadith 665