There is nothing in the sources of Shari`ah, as far as we know, necessitates sitting down while making ghusl (ritual bath).
In this regard, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “The proper method of ghusl (ritual bath) involves the following steps:
1. Make the niyyah (intention) to perform ghusl for purification.
2. Wash your private parts thoroughly with water.
3. Perform wudu’ (ablution) except for washing of your feet, which you can do later while bathing the body.
4. Wash the entire body, starting with your head and the right side, followed by the left.
5. It is preferred that the whole body be washed three times. The minimum is once.”