عَنْ أَنَسِ بْنِ مَالِكٍ رَضِيَ اللَّهُ عَنْهُ أَنَّ رَجُلًا جَاءَ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَدْ تَوَضَّأَ وَتَرَكَ عَلَى قَدَمِهِ مَوْضِعَ الظُّفْرِ فَقَالَ لَهُ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: ((ارْجِعْ فَأَحْسِنْ وَضُوءَكَ))
It is narrated from Sayyiduna Anas bin Malik, may Allah be pleased with him, that a man performed ablution and came to the Noble Prophet, peace and blessings be upon him, but there was a spot on his foot, the size of a fingernail, that remained dry. The Messenger of Allah, peace and blessings be upon him, said to him: "Go back and perform ablution properly."