Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
As long as you are unable to use water due to the doctor’s advice, you can perform dry ablution (tayammum) putting your hands on the dust or sand and wiping once on your face and another on your arms. In this case, you can go to the mosque and offer the Prayer.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states,
If you are told by your physician not to take a bath, you are allowed to perform tayammum (dry ablution) and pray. In this case, you are allowed to go to the mosque and pray after tayammum.
If, however, you are not advised by your physician against it, then you ought to perform ghusl before Prayer.
Prayer in this case is not valid without ghusl. Tayammum is allowed only when we are unable to use water for medical reasons or in case of not finding water.
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.