The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, narrated to me from Ahmad ibn Muhammad, from his father, from Muhammad ibn Yahya, and Al-Husayn ibn Ubayd Allah سبحانه وتعالى, from Ahmad ibn Muhammad ibn Yahya, from his father Muhammad ibn Yahya, from Muhammad ibn Ali ibn Mahbub, from Al-Husayn ibn Al-Hasan, from Ja'far ibn Bashir, from Isma'il Al-Ju'fi, from Abu Ja'far عليه السلام. He said: Imam عليه السلام said: "If blood is on the clothing, and it is less than the size of a dirham, then he does not need to repeat the prayer. But if it is more than the size of a dirham and he saw it but did not wash it before praying, then he must repeat his prayer. However, if he did not notice it until after praying, then he does not need to repeat the prayer."