Sunan an-Nasa'i 197
It was narrated from Umm Salamah that a woman said:
"O Messenger of Allah, Allah is not shy to tell the truth. Does a women have to perform Ghusl if she has a wet dream?" He said: "Yes, if she sees water."[1] Umm Salamah laughed and said: "Do women really have wet dreams?" The Messenger of Allah (ﷺ) said: "How else would her child resemble her?"
[1] That is, if she has an emission of the fluid of an orgasm.
أَخْبَرَنَا شُعَيْبُ بْنُ يُوسُفَ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ هِشَامٍ، قَالَ أَخْبَرَنِي أَبِي، عَنْ زَيْنَبَ بِنْتِ أُمِّ سَلَمَةَ، عَنْ أُمِّ سَلَمَةَ، أَنَّ امْرَأَةً، قَالَتْ يَا رَسُولَ اللَّهِ إِنَّ اللَّهَ لاَ يَسْتَحْيِي مِنَ الْحَقِّ هَلْ عَلَى الْمَرْأَةِ غُسْلٌ إِذَا هِيَ احْتَلَمَتْ قَالَ ‏"‏ نَعَمْ إِذَا رَأَتِ الْمَاءَ ‏"‏ ‏.‏ فَضَحِكَتْ أُمُّ سَلَمَةَ فَقَالَتْ أَتَحْتَلِمُ الْمَرْأَةُ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ فَفِيمَ يُشْبِهُهَا الْوَلَدُ ‏"‏ ‏.‏