Is it sufficient to perform ghusl by passing a sponge over the body while washing the hair under the tap or by running fingers through it?

It is sufficient in ghusl (ritual bath) for water to reach all parts of the body. Rubbing (dalak) is not obligatory according to the majority of scholars. So, if water is poured over the body and covers it entirely, the ghusl is valid. As for using a sponge alone without pouring water, it is not sufficient unless the sponge is squeezed and water flows from it onto the body.