She informed her, saying, "The Messenger of Allah ﷺ and I used to bathe from a single vessel, and I would say to him, 'Leave some for me, leave some for me.'"
حدثنا هاشم بن القاسم قال حدثنا المبارك قال حدثتني أمي عن معاذة العدوية
أنها أخبرتها قالت كنت أغتسل أنا ورسول الله ﷺ من إناء واحد وأنا أقول له أبق لي أبق لي
Its chain of transmission is sahih, it has occurred many times before. It is found in Muslim with its wording, 1/257, no. 321, in the chapter on menstruation, Nasai, 1/130, no. 239, in the chapter on purification, Humaydi, 1/90, no. 168, and Ibn Khuzayma, 1/118, no. 236.