It is clarified that wudu' is not required before or after the ghusl for janabah.

The Shaykh : The second benefit from this hadith is that it is not required to perform wudu' before the ghusl. It is not required to perform wudu' before the ghusl. So if a person immerses himself in water, immerses himself in a pool intending to perform ghusl for janabah, then comes out and rinses his mouth and sniffs water, is that sufficient or not? It is sufficient even if he did not perform wudu', because the Messenger of Allah (peace and blessings be upon him) did not tell this man to perform wudu'. If wudu' before ghusl had been obligatory, the Prophet (peace and blessings be upon him) would have made that clear.
We can take a third benefit from it, which is that if a person in a state of janabah intends only the ghusl, it suffices for the wudu'. If he intends only the ghusl and wudu' does not come to his mind, it suffices for him. This is correct, and it is indicated by the saying of Allah the Exalted: Even though this person in a state of janabah intends to stand up for prayer and he has not performed wudu', his ghusl for janabah suffices for him regarding the wudu'.