ENOfficial
Narrated Anas (rad): The Prophet (ﷺ) saw a man on whose foot appeared a portion like the size of a nail which was not touched by water. He then said, “Go back and perform your Wudu properly.” .
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَنَسٍ - رضى الله عنه - قَالَ: { رَأَى اَلنَّبِيُّ - صلى الله عليه وسلم -رَجُلًا, وَفِي قَدَمِهِ مِثْلُ اَلظُّفْرِ لَمْ يُصِبْهُ اَلْمَاءُ. فَقَالَ: "اِرْجِعْ فَأَحْسِنْ وُضُوءَكَ" } أَخْرَجَهُ أَبُو دَاوُدَ, وَالنَّسَائِيّ ُ 1 .
sunnah.com