كتاب الطهارة
2  
The Book of Purification
(32)
Chapter: The ruling on semen
(32)
باب حكْمِ الْمَنِيِّ ‏
Sahih Muslim 290

Abdullah b. Shihab al-Khaulani reported:

I stayed in the house of 'A'isha and had a wet dream (and perceived its effect on my garment), so (in the morning) I dipped both (the clothes) in water. This (act of mine) was watched by a maid-servant of A'isha and she informed her. She (Hadrat A'isha) sent me a message: Whatprompted you to act like this with your clothes? He (the narrator) said: I told that I saw in a dream what a sleeper sees. She said: Did you find (any mark of the fluid) on your clothes? I said: No. She said: Had you found anything you should have washed it. Incase I found that (semen) on the garment of the Messenger of Allah (ﷺ) dried up, I scraped it off with my nails.
وَحَدَّثَنَا أَحْمَدُ بْنُ جَوَّاسٍ الْحَنَفِيُّ أَبُو عَاصِمٍ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ شَبِيبِ بْنِ غَرْقَدَةَ، عَنْ عَبْدِ اللَّهِ بْنِ شِهَابٍ الْخَوْلاَنِيِّ، قَالَ كُنْتُ نَازِلاً عَلَى عَائِشَةَ فَاحْتَلَمْتُ فِي ثَوْبَىَّ فَغَمَسْتُهُمَا فِي الْمَاءِ فَرَأَتْنِي جَارِيَةٌ لِعَائِشَةَ فَأَخْبَرَتْهَا فَبَعَثَتْ إِلَىَّ عَائِشَةُ فَقَالَتْ مَا حَمَلَكَ عَلَى مَا صَنَعْتَ بِثَوْبَيْكَ قَالَ قُلْتُ رَأَيْتُ مَا يَرَى النَّائِمُ فِي مَنَامِهِ ‏.‏ قَالَتْ هَلْ رَأَيْتَ فِيهِمَا شَيْئًا ‏.‏ قُلْتُ لاَ ‏.‏ قَالَتْ فَلَوْ رَأَيْتَ شَيْئًا غَسَلْتَهُ لَقَدْ رَأَيْتُنِي وَإِنِّي لأَحُكُّهُ مِنْ ثَوْبِ رَسُولِ اللَّهِ صلى الله عليه وسلم يَابِسًا بِظُفُرِي ‏.‏
Reference : Sahih Muslim 290
In-book reference : Book 2, Hadith 140
USC-MSA web (English) reference : Book 2, Hadith 572
  (deprecated numbering scheme)