What is said when performing ghusl for janabah?

There is no ذكر (remembrance/supplication) to be recited when intending to perform ghusl other than saying "Bismillah" (in the name of Allah). The person performing ghusl must intend in their heart to lift the major ritual impurity (janabah), and it is not obligatory for them to vocalize the intention, as the Prophet, peace and blessings be upon him, said: "Actions are but by intentions."