The Prophet said: "If anyone of wakes up and sees some wetness, but he does not think that he had an erotic dream, let him have a bath. But if he thinks that he had an erotic dream but he does not see any wetness, then he does not have to take a bath."
عَنِ النَّبِيِّ ﷺ قَالَ إِذَا اسْتَيْقَظَ أَحَدُكُمْ مِنْ نَوْمِهِ فَرَأَى بَلَلاً وَلَمْ يَرَ أَنَّهُ احْتَلَمَ اغْتَسَلَ وَإِذَا رَأَى أَنَّهُ قَدِ احْتَلَمَ وَلَمْ يَرَ بَلَلاً فَلاَ غُسْلَ عَلَيْهِ
[Machine] On the authority of the Prophet ﷺ, regarding a man who wakes up and sees wetness without remembering having a dream, he said, "Let him perform Ghusl (ritual bath) if he sees a wet dream but does not see any wetness, then there is no obligation for him to perform Ghusl."
عَنِ النَّبِيِّ ﷺ فِي الرَّجُلِ يَسْتَيْقِظُ فَيَرَى بَلَلًا وَلَمْ يَذْكُرِ احْتِلَامًا قَالَ «لِيَغْتَسِلْ فَإِنْ رَأَى احْتِلَامًا وَلَمْ يَرَ بَلَلًا فَلَا غُسْلَ عَلَيْهِ»
The Prophet said: "If anyone of wakes up and sees some wetness, but he does not think that he had an erotic dream, let him have a bath. But if he thinks that he had an erotic dream but he does not see any wetness, then he does not have to take a bath." (Using translation from Ibn Mājah 612)
"إِذَا استيقظ أحدُكم من نومِه فرأى بَلَلًا، ولم يَر أنَّهُ احتلمَ اغتسلَ، وإذا رأى أنهُ قدْ احتلمَ ولمْ يَرَ بَللًا فلا غُسلَ عليه".