Hadith: Man's discharge (i. e. semen) is thick and white, and the discharge (vaginal fluid) of a woman is thin and yellow, and the resemblance (of the child) comes from the one that dominates or precedes

عن أنس بن مالك رضي الله عنه : أن أم سُلَيم حدَّثَت أنَّها سألت نَبِي الله صلى الله عليه وسلم عن المرأة تَرى في مَنَامِها ما يَرى الرَّجل، فقال رسول الله صلى الله عليه وسلم : «إذا رَأَت ذلك المرأة فَلْتَغْتَسِل» فقالت أم سُلَيْم: واسْتَحْيَيْتُ من ذلك، قالت: وهل يَكون هذا؟ فقال نَبِي الله صلى الله عليه وسلم : «نعم، فمِن أين يَكُون الشَّبَه؟ إنَّ ماء الرَّجُل غَليِظ أبْيَض، وماء المرأة رقِيق أصْفَر، فَمِنْ أَيِّهِمَا عَلَا، أو سَبَقَ، يَكُونُ مِنْه الشَّبَهُ».
[صحيح] - [رواه مسلم]

Anas ibn Mālik (may Allah be pleased with him) reported that Umm Sulaym said that she asked the Messenger of Allah (may Allah's peace and blessings be upon him) about a woman who sees in a dream what a man sees (a wet dream). The Messenger of Allah (may Allah's peace and blessings be upon him) replied: "If the woman sees that, she must take a ritual bath." Umm Sulaym said: "I was bashful on account of that and said: 'Does that happen?'" Upon this, the Prophet (may Allah's peace and blessings be upon him) said: "Yes (it does happen), otherwise where does resemblance come from? Man's discharge (i. e. semen) is thick and white, and the discharge (vaginal fluid) of a woman is thin and yellow, and the resemblance (of the child) comes from the one that dominates or precedes."
[Authentic hadith] - [Narrated by Muslim]

Explanation

Anas ibn Mālik (may Allah be pleased with him) informs us about his mother, Umm Sulaym (may Allah be pleased with her) that she asked the Prophet (may Allah’s peace and blessings be upon him) about a woman who sees what a man sees while dreaming; meaning: a wet dream. The Prophet (may Allah’s peace and blessings be upon him) replied: "If the woman sees that, she must take a ritual bath;" meaning: if a woman has a wet dream in her sleep, then she must take a bath. What is meant here is if she sees the vaginal fluid, as mentioned in Al-Bukhāri: "He said: 'Yes, if she sees the vaginal fluid;'" meaning: seeing it after waking up. However, if she has a wet dream but does not see any vaginal fluid, then she will not have to take a bath, because the ruling of making ritual bath is conditional upon the discharge of the vaginal fluid. Hence, when the Prophet (may Allah's peace and blessings be upon him) was asked about a man who finds himself wet and does not recall having a wet dream, he said: "Let him make ritual bath." Regarding the man who recalls having a wet dream but does not find semen, he said: "He does not have to take a ritual bath." So Umm Sulaym said: "If a woman sees that, does she have to bathe?" He replied: "Yes, women are peers to men." [Ahmad and Abu Dawūd] When Umm Sulaym heard the response from the Messenger of Allah (may Allah's peace and blessings be upon him) she was bashful and asked: "Does that happen?" Meaning: is it possible that a woman has a wet dream and that she wets herself like a man does? The Prophet of Allah (may Allah's peace and blessings be upon him) said: 'Yes'; meaning: yes, this occurs to a woman just as it occurs to a man. Then he justified that, saying: "Otherwise, where does resemblance come from?" Another narration in the two Sahīhs reads: "How does her child resemble her?" Meaning: so where does the resemblance of the child to his mother come from if she does not discharge vaginal fluid? Then the Prophet (may Allah's peace and blessings be upon him) clarified the description of the man’s discharge and the woman’s discharge to her, saying: "Man's discharge (semen) is thick and white, and the discharge (vaginal fluid) of a woman is thin and yellow." This description is based upon what it is normally and in case of healthiness, because the discharge of the man could be thin if he is sick, or reddish in color if he has sexual intercourse a lot, and a woman’s discharge could be white because of her strength. Scholars, may Allah have mercy upon them, mentioned that the discharge of the man has other descriptions which it can be recognized from, such as its flowing out one time after another, and the Qur'an has referred to this, as Allah says: {He is created from a water gushing forth} [Sūrat At-Tāriq: 6]. It comes out with desire and pleasure, and after it comes out, one feels exhausted and tired. It has a smell like that of a date palm, which is similar to the smell of dough. As for the discharge of the woman, scholars said that it has two main characteristics from which it could be recognized: it smells like man's semen, and the woman experiences pleasure while it comes out, and her desire decreases after its release. It is not conditional in establishing whether it is sexual discharge or not that all these characteristics are present; rather, one characteristic is enough to determine if it is sexual discharge or not, and if none of these characteristics is there, then one cannot say that it is sexual discharge, and it most probably is not. "The resemblance comes from the one that dominates or precedes." In another narration: "that is more;" meaning: if the sexual discharge of one of them is more than the other, either in quantity or strength, then the resemblance of the child will be for that person, or if the discharge of one of them precedes the other, then the resemblance of the child will be for the one who preceded the other in discharging the sexual fluid. Some of the scholars said that "the one that dominates" means precedes. If the discharge of the man precedes, then the child will resemble him, and if the woman’s discharge precedes, then the child will resemble her. This is because the man's semen and the woman's vaginal fluid are combined in the womb; both of them release their sexual fluid, and from their mixing, the fetus is created. For this reason, Allah says: {Indeed, We created man from a sperm-drop mixture} [Sūrat al-Insān: 1-2]; meaning: mixed from the male and female sexual discharges.