A man came to the Prophet ﷺ after performing his ablution, but he had left a spot on his foot the size of a fingernail untouched by water. The Messenger of Allah ﷺ said to him, "Go back and perform your ablution properly."
حدثنا هارون بن معروف حدثنا ابن وهب عن جرير بن حازم أنه سمع قتادة بن دعامة
أن رجلا جاء إلى النبي ﷺ وقد توضأ وترك على قدمه مثل موضع الظفر فقال له رسول الله ﷺ ارجع فأحسن وضوءك
[Sahih] Ibn Majah reported it in Kitab al-Tahara, chapter on one who performs wudu but leaves a spot untouched by water, no. 665, from the hadith of Abdullah bin Wahb through this route, and Ibn Khuzayma graded it sahih, no. 164.