Salamah ibn Shabib narrated to me: al-Hasan ibn Muhammad ibn A‘yan narrated to us: Ma‘qil narrated to us, from Abu al-Zubayr, from Jabir: ‘Umar ibn al-Khattab informed me that a man performed ablution and left a spot the size of a nail on his foot. The Prophet, peace and blessings be upon him, saw it and said: "Go back and perform your ablution properly." So he went back, then prayed.