Ibn Hazm on wudū with leftover

“Case 151: And every water that a woman did make wudū with – whether she is in her menstruating period or not in her menstruating period – or when she did take a ritual bath (ghusl) from it, that resulted in a leftover (of water), then it is not permissible for a man to make wudū from this leftover and neither a ghusl from it, whether they find new water or nothing but the leftover, and then it becomes obligatory for them to make tayamum, and it is permissible to drink from it for men as well as women, and it is permissible for women to make wudū with it and ghusl in every circumstance. And it will not be seen as a leftover except when it is less than what she had used from it, when it is the same amount or more; then it will not be seen as a leftover, and then wudū and ghusl with it is permissible for men and women.

As for the leftover of men, then making wudū with it and ghusl is permissible for the man and the woman, except when there is a narration on the forbiddance upon the woman, then I will stop at that, and I did not find it authentic. When a man and a woman make wudū from one vessel or make ghusl from one vessel that they share, this is permissible, without consideration who began first, or who ended first.”

End of translation.

Source: Al-Muhallā (fi sharh al-majallā bi al-hujaj wal athār) of Abu Muhamad ‘Alī bin Ahmad bin Sa’īd bin Hazm al-Andalusī rahimahullāh, 1/170