Mishkat al-Masabih 3 Purification كتاب الطهارة 137

وَقَالَ ابْنُ عَبَّاسٍ: إِنَّمَا الْمَاءُ مِنَ الْمَاءِ فِي الِاحْتِلَامِ. رَوَاهُ التِّرْمِذِيُّ وَلَمْ أَجِدْهُ فِي الصَّحِيحَيْنِ

Ibn ‘Abbas said that “Water is necessary only when there is an emission” applies to a dream. Tirmidhi transmitted it, but I have not found it in the two Sahihs .