In case a woman sees that, she must take a bath. Umm Sulaim said: I was bashful on account of that and said: Does it happen? Upon this the Messenger of Allah ﷺ said: Yes (it does happen), otherwise how can (a child) resemble her? Man's discharge (i. e. sperm) is thick and white and the discharge of woman is thin and yellow; so the resemblance comes from the one whose genes prevail or dominate. (Using translation from Muslim 311)   

أَنَّهَا سَأَلَتْ رَسُولَ اللهِ ﷺ عَنِ الْمَرْأَةِ تَرَى فِي مَنَامِهَا مَا يَرَى الرَّجُلُ فِي مَنَامِهِ فَقَالَ رَسُولُ اللهِ ﷺ إِذَا رَأَتْ ذَلِكَ الْمَرْأَةُ فَلْتَغْتَسِلْ فَقَالَتْ أُمُّ سَلَمَةَ وَاسْتَحْيَيْتُ مِنْ ذَلِكَ قَالَتْ وَهَلْ يَكُونُ هَذَا؟ فَقَالَ رَسُولُ اللهِ ﷺ فَمِنْ أَيْنَ يَكُونُ الشَّبَهُ إِنَّ مَاءَ الرَّجُلِ غَلِيظٌ أَبْيَضُ وَمَاءُ الْمَرْأَةِ رَقِيقٌ أَصْفَرُ فَمِنْ أَيِّهِمَا عَلَا أَوْ سَبَقَ يَكُونُ مِنْهُ الشَّبَهُ لَفْظُ حَدِيثِ الْعَبَّاسِ  

While I was standing beside the Messenger of Allah ﷺ one of the rabbis of the Jews came and said: Peace be upon you, O Muhammad. I pushed him backwith a push that he was going to fall. Upon this he said: Why do you push me? I said: Why don't you say: O Messenger of Allah? The Jew said: We call him by the name by which he was named by his family. The Messenger of Allah ﷺ said: My name is Muhammad with which I was named by my family. The Jew said: I have come to ask you (something). The Messenger of Allah ﷺ said: Should that thing be of any benefit to you, if I tell you that? He (the Jew) said: I will lend my ears to it. The Messenger of Allah ﷺ drew a line with the help of the stick that he had with him and then said: Ask (whatever you like). Thereupon the Jew said: Where would the human beings be on the Daywhen the earth would change into another earth and the heavens too (would change into other heavens)? The Messenger of Allah ﷺ said: They would be in darkness beside the Bridge. He (the Jew) again said: Who amongst people would be the first to cross (this bridge).? He said: They would be the poor amongst the refugees. The Jew said: What would constitute their breakfast when they would enter Paradise? He (the Holy Prophet) replied: A caul of the fish-liver. He (the Jew) said. What would be their food alter this? He (the Holy Prophet) said: A bullockwhich was fed in the different quarters of Paradise would be slaughtered for them. He (the Jew) said: What would be their drink? He (the Holy Prophet) said: They would be given drink from the fountain which is named" Salsabil". He (the Jew) said: I have come to ask you about a thing which no one amongst the people on the earth knows except an apostle or one or two men besides him. He (the Holy Prophet) said: Would it benefit you if I tell you that? He (the Jew) said: I would lend ears to that. He then said: I have come to ask you about the child. He (the Holy Prophet) said: The reproductive substance of man is white and that of woman (i. e. ovum central portion) yellow, and when they have sexual intercourse and the male's substance (chromosomes and genes) prevails upon the female's substance (chromosomes and genes), it is the male child that is created by Allah's Decree, and when the substance of the female prevails upon the substance contributed by the male, a female child is formed by the Decree of Allah. The Jew said: What you have said is true; verily you are an Apostle. He then returned and went away. The Messenger of Allah ﷺ said: He asked me about such and such things of which I have had no knowledge till Allah gave me that. (Using translation from Muslim 315a)   

أَنَّ ثَوْبَانَ مَوْلَى رَسُولِ اللهِ ﷺ قَالَ كُنْتُ قَائِمًا عِنْدَ رَسُولِ اللهِ ﷺ فَجَاءَ حَبْرٌ مِنْ أَحْبَارِ الْيَهُودِ فَقَالَ السَّلَامُ عَلَيْكَ يَا مُحَمَّدُ قَالَ فَدَفَعْتُهُ دَفْعَةً كَادَ يُصْرَعُ مِنْهَا فَقَالَ الْيَهُودِيُّ لِمَ دَفَعْتَنِي؟ فَقُلْتُ أَلَا تَقُولُ يَا رَسُولَ اللهِ قَالَ الْيَهُودِيُّ إِنَّمَا نَدْعُوهُ بِاسْمِهِ الَّذِي سَمَّاهُ بِهِ أَهْلُهُ فَقَالَ رَسُولُ اللهِ ﷺ إِنَّمَا اسْمِي الَّذِي سَمَّانِي بِهِ أَهْلِي مُحَمَّدٌ قَالَ الْيَهُودِيُّ جِئْتُ أَسْأَلُكَ عَنْ شَيْءٍ فَقَالَ رَسُولُ اللهِ ﷺ أَيَنْفَعُكَ شَيْءٌ إِنْ حَدَّثْتُكَ قَالَ أَسْمَعُ بِأُذُنِي فَنَكَتَ رَسُولُ اللهِ ﷺ بِعُودٍ مَعَهُ ثُمَّ قَالَ سَلْ فَقَالَ الْيَهُودِيُّ أَيْنَ يَكُونُ النَّاسُ يَوْمَ تُبَدَّلُ الْأَرْضُ غَيْرَ الْأَرْضِ وَالسَّمَاوَاتُ؟ فَقَالَ رَسُولُ اللهِ ﷺ هُمْ فِي الظُّلْمَةِ دُونَ الْجِسْرِ قَالَ فَمَنْ أَوَّلُ النَّاسِ إِجَازَةً؟ قَالَ فُقَرَاءُ الْمُهَاجِرِينَ قَالَ الْيَهُودِيُّ فَمَا تُحْفَتُهُمْ حِينَ يَدْخُلُونَ الْجَنَّةَ؟ قَالَ زِيَادَةُ كَبِدِ النُّونِ قَالَ فَمَا غِذَاؤُهُمْ عَلَى إِثْرِهَا؟ قَالَ يُنْحَرُ لَهُمْ ثَوْرُ الْجَنَّةِ الَّذِي كَانَ يَأْكُلُ مِنْ أَطْرَافِهَا قَالَ فَمَا شَرَابُهُمْ عَلَيْهِ؟ قَالَ مِنْ عَيْنٍ فِيهَا تُسَمَّى سَلْسَبِيلًا فَقَالَ صَدَقْتَ قَالَ وَجِئْتُ أَسْأَلُكَ عَنْ شَيْءٍ لَا يَعْلَمُهُ أَحَدٌ مِنْ أَهْلِ الْأَرْضِ إِلَّا نَبِيٌّ أَوْ رَجُلٌ أَوْ رَجُلَانِ قَالَ أَيَنْفَعُكَ إِنْ حَدَّثْتُكَ قَالَ أَسْمَعُ بِأُذُنِي قَالَ جِئْتُ أَسْأَلُكَ عَنِ الْوَلَدِ؟ فَقَالَ النَّبِيُّ ﷺ مَاءُ الرَّجُلِ أَبْيَضُ وَمَاءُ الْمَرْأَةِ أَصْفَرُ فَإِذَا عَلَا مَنِيُّ الرَّجُلِ مَنِيَّ الْمَرْأَةِ أَذْكَرَا بِإِذْنِ اللهِ تَعَالَى وَإِذَا عَلَا مَنِيُّ الْمَرْأَةِ مَنِيَّ الرَّجُلِ آنَثَا بِإِذْنِ اللهِ فَقَالَ صَدَقْتَ وَإِنَّكَ لِنَبِيٌّ ثُمَّ انْصَرَفَ فَقَالَ النَّبِيُّ ﷺ لَقَدْ سَأَلَنِي هَذَا عَنِ الَّذِي سَأَلَنِي عَنْهُ وَمَا لِي بِشَيْءٍ مِنْهُ عَلِمٌ حَتَّى آتَانِي اللهُ بِهِ