How can one reconcile the Hadith about the Prophet's ritual bathing (ghusl) using the leftover water of Maymunah, and his prohibition against a man performing ghusl with the leftover water of a woman or vice versa, with the Hadith, "Water does not become ritually impure (junub)"?

The narrations regarding a man performing ablution (wudu') with the leftover water (fadl) from a woman's ablution differ in two ways:

The first way: Narrations indicating its permissibility. The majority of scholars, such as the Hanafis, Malikis, Shafi'is, and one narration from Imam Ahmad, have adopted this view. Among these is the account of the Prophet (peace be upon him) and 'Aisha (may Allah be pleased with her) performing ghusl (definition) from a single vessel, where each would perform ghusl with the leftover water of the other.

The second way: Narrations prohibiting it. Some Companions and Tabi'un, such as Ibn 'Umar and Al-Hasan (definition) Al-Basri, and the Hanbalis in the relied-upon position of their madhhab (definition), have adopted this view. Among these is the Prophet's (peace be upon him) prohibition of a man performing ablution with the leftover water from a woman's purification. Scholars have differed on the authenticity of these narrations; some have deemed them good (hasan), while others have deemed them weak.

Al-Nawawi responded to the prohibiting narrations by stating that they are either weak, or they are to be understood as a prohibition concerning the water that flowed off her limbs, or that the prohibition is for discouragement (tanzih) and not for outright prohibition (tahrim). This third answer is the relied-upon one, meaning that it is preferable for a man not to perform ablution with the leftover water from a woman's purification, but if he does, his ablution is permissible and valid.