What is the ruling on washing only the glans of the penis after urination if the body is already wet before performing ghusl, and does the ruling differ if one has finished washing the glans and testicles and then urinated?

In istinja' (purification after defecation or urination), one must have a strong conviction that the impurity has been removed. The criterion for this, when using water, is the return of the area to its original state before relieving oneself. When using stones, it is the last stone emerging clean. It is not obligatory to wash anything beyond the contaminated area unless the impurity spreads to it, in which case it must be purified with water.