عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «إِذا جلس بَيْنَ شُعَبِهَا الْأَرْبَعِ ثُمَّ جَهَدَهَا فَقَدْ وَجَبَ الْغسْل وَإِن لم ينزل»

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.