What is the ruling on someone who finds a small spot of adhesive material on one of their fingers after performing ghusl for janabah, without knowing whether it was there before or after the ghusl, and is it obligatory for them to repeat the ghusl?

For ablution (tahara) to be valid, anything that prevents water from reaching the skin must be removed. If someone performs a ritual bath (ghusl) or ablution (wudu) and then sees an adhesive substance but does not know when it appeared, the default assumption is that it appeared after the purification, because "a new occurrence is attributed to the nearest of its times." Therefore, repeating the ghusl is not necessary.

Some scholars have excused a small obstruction, whether it is under the nails or anywhere else on the body. This is the choice of Sheikh al-Islam Ibn Taymiyyah. And assuming that the adhesive substance was present before the ghusl, and that a small obstruction is not excused, then repeating the ghusl is not obligatory; rather, it suffices to remove the spot and then wash the area beneath it.