What is the ruling on one who made a covenant with Allah to abandon masturbation, then returned to it? And is an expiation for breaking an oath obligatory upon him?

According to the preponderant opinion, an expiation for a broken oath (kaffarat yamin) is required when violating a covenant made with Allah Almighty. As for the statement "I call Allah to witness," it does not necessitate expiation unless the person intended it as an oath. Therefore, pay the expiation for breaking an oath, strive against your soul to abandon sin, and increase in supplication.