What is the ruling on masturbation, and is it forbidden and considered a form of zina, or is it a sin, especially after repeated occurrences despite swearing on the Qur’an to abandon it?

Breaking an oath sworn on the Qur'an and violating a pledge to abandon masturbation does not place its perpetrator among the ranks of disbelievers. Masturbation is forbidden, but its prohibition does not reach the level of zina (fornication/adultery); it is one of many sins. Efforts must be made to quit it. What helps in this regard are marriage, increasing voluntary fasting, staying away from provocations, occupying one's time and mind with knowledge and da'wah (calling to Islam), and accompanying righteous people.