[A.] Whoever has a wet dream there is nothing upon him, because wet dreams are not by choice, so does not ruin his fast. Likewise, the pilgrim’s state of ritual consecration (Iḥrām) is not ruined, because wet dreams are unintentional and he conforms to it without choice. However, it is obligatory upon him to make ghusl from sexual impurity (janābah).

Reference: http://www.alfawzan.af.org.sa/node/14891]