Is it necessary to urinate before performing ghusl for janabah?

Urination before ghusl (ritual bath) for janabah (state of ritual impurity requiring ghusl) is not obligatory, and the presence of semen in the vagina does not affect the validity of ghusl, because it is considered internal. There is no mention in the descriptions of the Prophet's ghusl (peace and blessings of Allah be upon him) that he would urinate before ghusl; rather, he would wash his private parts and then perform ablution (wudu') as he would for prayer. If one does urinate before ghusl, it is good, as there is a possibility of residual semen being expelled with the urine. If semen is discharged after ghusl, ablution is invalidated, but ghusl does not need to be repeated.