Narrated by:'Umar bin Khattab said
It was narrated that 'Umar bin Khattab said:"The Messenger of Allah saw a man performing ablution and he missed a spot the size of a fingernail on his foot. He commanded him to repeat the ablution and his prayer, so he did."
حَدَّثَنَا حَرْمَلَةُ بْنُ يَحْيَى، حَدَّثَنَا ابْنُ وَهْبٍ، ح وَحَدَّثَنَا ابْنُ حُمَيْدٍ، حَدَّثَنَا زَيْدُ بْنُ الْحُبَابِ، قَالاَ حَدَّثَنَا ابْنُ لَهِيعَةَ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، عَنْ عُمَرَ بْنِ الْخَطَّابِ، قَالَ رَأَى رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ رَجُلاً تَوَضَّأَ فَتَرَكَ مَوْضِعَ الظُّفْرِ عَلَى قَدَمِهِ فَأَمَرَهُ أَنْ يُعِيدَ الْوُضُوءَ وَالصَّلاَةَ . قَالَ فَرَجَعَ .
IbnMaja
The Book of Purification and its Sunnah • Hadith 666