Does the persistence of soap residue on the body after washing, despite water reaching it, invalidate the completion of ghusl and necessitate redoing it?

There is no harm in using soap, shampoo, Sidr (lote tree leaves), and similar items when performing ghusl (ritual bath) from janabah (state of ritual impurity). This suffices for wudu' (ablution) if both purifications are intended. It is preferable to perform wudu' first, then ghusl.

If, after ghusl, the person finds some soap on their body, it does not harm them if they had poured water over their body with the intention of removing the hadath (ritual impurity) before using the soap, or if the water was mixed with it.

However, if they did not pour water over their body with the intention of removing the hadath until after using the soap, then if the soap found was not an impediment preventing water from reaching the skin, their ghusl is valid. But if it was an impediment, they must wash that specific spot after removing the impediment, and they are not required to repeat the entire ghusl. If they had prayed with this ghusl, they must repeat the prayer.