Is it necessary to repeat the entire ghusl, or is it sufficient to wash the area of the barrier if the one performing ghusl discovers it some time after completing the ghusl?

For ablution (wudu') and ritual bath (ghusl) to be valid, all barriers preventing water from reaching the skin must be removed. If someone performing ghusl leaves a part of their body untouched by water, or if there is a barrier preventing water from reaching it, and then they realize this, they are not required to repeat the entire ghusl. Rather, it suffices for them to wash only the part that was not touched by water. This is because the majority of scholars do not consider continuity (muwalat) obligatory in ghusl. Sheikh al-Islam Ibn Taymiyyah supported this with several proofs, including: what was narrated about the Prophet (peace be upon him) that he squeezed his hair over a dry spot he noticed after his ghusl; the statement of Ali (may Allah be pleased with him) to someone who noticed a fingernail-sized spot not touched by water, "Had you wiped over it with your hand, it would have sufficed you"; that major ritual impurity (janabah) is reduced by performing wudu'; Ibn Abbas's statement concerning someone who forgot to rinse their mouth and nose during janabah, that they should go and rinse their mouth and nose and repeat the prayer; that continuity is subsidiary to order; and that separating the ghusl is often necessary.