"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."
رَأَى رَسُولُ اللَّهِ ﷺ رَجُلاً تَوَضَّأَ فَتَرَكَ مَوْضِعَ الظُّفْرِ عَلَى قَدَمِهِ فَأَمَرَهُ أَنْ يُعِيدَ الْوُضُوءَ وَالصَّلاَةَ قَالَ فَرَجَعَ