Is sin in masturbation considered to be by ejaculation or merely by engaging in the act, and is a person punished for merely engaging in it without ejaculating?

The sin of masturbation lies in the act itself. So, if a person masturbates with his hand, even if he does not ejaculate, he has sinned, and he must repent. Masturbation is forbidden and harmful to both mental and physical health. Whoever is afflicted by it must stop immediately.