I met a man who accompanied the Prophet ﷺ for four years, just as Abu Hurairah accompanied him. He said, "The Messenger of Allah ﷺ forbade that a woman bathe with the leftover water of a man, or that a man bathe with the leftover water of a woman. Rather, let them both scoop from it together."
لقيت رجلا صحب النبي ﷺ أربع سنين، كما صحبه أبو هريرة، قال: نهى رسول الله ﷺ أن تغتسل المرأة بفضل الرجل، أو يغتسل الرجل بفضل المرأة، وليغترفا جميعا.
Abu Dawud (81) and Nasai (238) both narrated it through the route of Abu Awana, from Dawud Awdi, from Humayd bin Abdul-Rahman, who said, and he mentioned the hadith. Its chain is sahih, and Dawud bin Abdullah Awdi, even though Bukhari and Muslim did not use him as a source, is nonetheless trustworthy. Ibn Main, Ahmad bin Hanbal, and Nasai all declared him trustworthy.However, Bayhaqi (1/190) said, "The narrators of this hadith are trustworthy, except that Humayd did not name the companion who related it to him, so it carries the sense of a mursal narration, though it is a good mursal, were it not for its contradiction of the established, connected hadiths that precede it. And Dawud bin Abdullah Awdi was not used as a source by Bukhari and Muslim."The Hafiz responded to this in Fath al-Bari (1/300), after stating that its narrators are trustworthy and that he had found no strong evidence for anyone who declared it defective. He said that Bayhaqi's claim that it carries the sense of a mursal narration is to be rejected, because the companion's being unnamed does not harm the narration, since the successor explicitly stated that he had met him. He also rejected Ibn Hazm's claim that the Dawud who narrated from Humayd bin Abdul-Rahman is Dawud bin Yazid Awdi, who is daif. Rather, he is Dawud bin Abdullah Awdi, who is trustworthy, and Abu Dawud and others have explicitly stated the name of his father. End of quote.