What was narrated to me by the Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, from Ahmad ibn Muhammad, from his father, from al-Husayn ibn al-Hasan ibn Aban, from al-Husayn ibn Sa‘id, from Ya‘qub ibn Yaqtin, who said: I asked Abu al-Hasan عليه السلام about a man who performed tayammum and prayed, and then after his prayer found water. Should he perform ablution (wudu’) and repeat the prayer, or is his prayer valid? Imam عليه السلام said: "If he finds water before the time for the prayer has passed, he should perform ablution and repeat the prayer. However, if the time has passed, there is no need to repeat it."