What is the ruling on one who masturbates in Ramadan or on any other obligatory fast, intentionally doing so, knowing that the time for fasting has begun, but forgetting that he is fasting?

Intentional masturbation is forbidden and invalidates the fast, whether it is an obligatory or a supererogatory fast. However, if a fasting person does it out of forgetfulness, their fast is valid according to many scholars, based on the Prophet Muhammad’s (peace be upon him) saying: "My nation has been forgiven for mistakes, forgetfulness, and what they are forced to do."