What is the ruling on the involuntary emission of semen, and what are the ways to avoid prohibited sexual thoughts?

Engaging with and intentionally dwelling on lustful thoughts is impermissible because it is a gateway to evil. It is obligatory to distance oneself from that. However, if such thoughts overcome you without any conscious summoning on your part, then there is no sin upon you. Intentionally causing semen to be emitted through thought falls under the forbidden act of masturbation. It is recommended to engage in beneficial activities, occupy free time with the remembrance of Allah and the recitation of His Book, and strive in supplication. Guarding one's thoughts is important because dwelling on evil thoughts can lead to the forbidden, corrupt the heart, and waste time.