(1) The Book of Purification and its Sunnah
كتاب الطهارة وسننها
(112) Chapter: One who had an erotic dream but did not see any wetness
(112) باب مَنِ احْتَلَمَ وَلَمْ يَرَ بَلَلاً
Sunan Ibn Majah 612 
It was narrated from 'Aishah that:
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."
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا حَمَّادُ بْنُ خَالِدٍ، عَنِ الْعُمَرِيِّ، عَنْ عُبَيْدِ اللَّهِ، عَنِ الْقَاسِمِ، عَنْ عَائِشَةَ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ ‏ "‏ إِذَا اسْتَيْقَظَ أَحَدُكُمْ مِنْ نَوْمِهِ فَرَأَى بَلَلاً وَلَمْ يَرَ أَنَّهُ احْتَلَمَ اغْتَسَلَ وَإِذَا رَأَى أَنَّهُ قَدِ احْتَلَمَ وَلَمْ يَرَ بَلَلاً فَلاَ غُسْلَ عَلَيْهِ ‏"‏ ‏.‏
Grade :  Da'if (Darussalam)
Reference : Sunan Ibn Majah 612
In-book reference : Book 1, Hadith 346
English translation : Vol. 1, Book 1, Hadith 612