Is it permissible to perform ablution (Wudu') instead of the major ritual bath (Ghusl) after masturbating due to embarrassment from one's wife, knowing that water is available and that masturbation is forbidden, but its prohibition is less severe than that of Zina (fornication/adultery)?

If masturbation leads to the emission of semen, then ghusl (ritual bath) becomes obligatory, based on the Prophet's (PBUH) sayings: "Water is from water" and "If you gush forth water, then perform ghusl." Every prayer performed after ejaculation without ghusl is invalid and must be repeated. Repentance is obligatory for this and for masturbation. Shyness from one's wife does not justify abandoning the obligatory ghusl, because Allah is more deserving of shyness. The wife must fulfill her husband's needs to the best of her ability.