The World Federation One Stop Fiqh

Ruling 1569

Whenever a fasting person knows that if he goes to sleep during the day he will have a wet dream [i.e. become muḥtalim] – meaning that semen will be ejaculated in his sleep – it is permitted (jāʾiz) for him to go to sleep even if he will not encounter difficulty by not sleeping; and if he has a wet dream, his fast does not become invalid.