His mother Umm Sulaym asked the Messenger of Allah ﷺ, "If a woman sees in her dream what a man sees, what should she do?"He replied, "If she sees that in her dream, let her perform a full bath."Umm Salama, the wife of the Prophet ﷺ, asked with embarrassment, "Does this really happen, Messenger of Allah?"He answered, "Yes. Otherwise, how would the resemblance come about? The man's fluid is white and thick, while the woman's fluid is yellow and thin. Whichever of the two precedes or prevails, the child resembles that parent."
حدثنا محمد بن جعفر حدثنا سعيد عن قتادة
أن أمه أم سليم سألت رسول الله ﷺ قالت المرأة ترى في منامها ما يرى الرجل فقال إذا رأت ذلك في منامها فلتغتسل فقالت أم سلمة زوج النبي ﷺ واستحيت أويكون هذا يا رسول الله قال نعم فمن أين يكون الشبه ماء الرجل أبيض غليظ وماء المرأة أصفر رقيق فمن أيهما سبق أو علا يكون الشبه
Its chain of transmission is sahih. It has preceded many times, and its wording is found in Muslim 1/250, no. 311, in the book of menstruation, on the description of a man's semen, and in Nasai 1/115, no. 197, in the book of purification, on a woman's ghusl.