Sunan an-Nasa'i 200
It was narrated that Anas said:
"The Messenger of Allah (ﷺ) said: 'The man's water is thick and white, and the woman's water is thin and yellow. Whichever of them comes first, the child will resemble (that parent).'"
أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا عَبْدَةُ، قَالَ حَدَّثَنَا سَعِيدٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ مَاءُ الرَّجُلِ غَلِيظٌ أَبْيَضُ وَمَاءُ الْمَرْأَةِ رَقِيقٌ أَصْفَرُ فَأَيُّهُمَا سَبَقَ كَانَ الشَّبَهُ ‏"‏ ‏.‏