Does a wet dream affect fasting, and is there a sin incurred by someone who has a wet dream in the mosque, and how can this be avoided in the future?

Nocturnal emission (ihtilam) does not affect the validity of the fast, as the Prophet, peace and blessings be upon him, said: "The pen has been lifted from three: from the insane person until he recovers, from the sleeper until he awakens, and from the child until he reaches puberty." Therefore, there is no expiation (kaffarah) upon you, nor any sin. It is advisable to avoid sleeping in the mosque to prevent the recurrence of nocturnal emission there.