The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: It is not permissible to purify oneself with water that has been used in washing impurities such as menstruation, irregular bleeding, postpartum bleeding, Janabah (major ritual impurity), or washing the dead. However, it is permissible to purify oneself with water that has been used for washing the face and hands in Wudu' for prayer, or water used for washing pure bodies in acts of recommended purification, such as the Ghusl of Friday or Eid. Nonetheless, it is better to seek out pure water that has not been used in performing either obligatory or recommended acts, as we have explained. This ruling is based on the principle that a person is obligated to perform ablution only with water whose purity is certain, ensuring that prayer becomes permissible through its use. Water used for Ghusl from Janabah carries doubt about its purity, and thus its use should not be allowed. This is further supported by evidence.
Commentary #7