Al-Kāfi - Volume 3 > Wet Dreams of Men and Women
Hadith #2

2ـ مُحَمَّدُ بْنُ إِسْمَاعِيلَ عَنِ الْفَضْلِ بْنِ شَاذَانَ عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ مُعَاوِيَةَ بْنِ عَمَّارٍ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ سَأَلْتُهُ عَنْ رَجُلٍ احْتَلَمَ فَلَمَّا انْتَبَهَ وَجَدَ بَلَلاً فَقَالَ لَيْسَ بِشَيْ‏ءٍ إِلاَّ أَنْ يَكُونَ مَرِيضاً فَعَلَيْهِ الْغُسْلُ.

2. Muhammad ibn ’Isma‘il has narrated from al-Fadl ibn Shadhan from ibn abu ‘Umayr from Mu‘awiyah ibn ‘Ammar who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about a man who dreams and when he wakes up finds moisture and wet spots. He (the Imam) said, ‘It is not necessary to do anything unless he suffers from an illness in which case he must take Ghusl (bath).”’ (Fatwa best explains this Hadith.)