I am a married woman. Sometimes, when I am in a state of Janaabah, I do not perform the Fajr prayer in its due time because making Ghusl during the night causes me health problems. What is the Sharee‘ah ruling? Am I required to make Ghusl during the night in order to perform the Fajr prayer in its due time? Is it permissible to delay Ghusl until the morning in order to avoid the consequent health problems?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

You are required to make Ghusl before the Fajr prayer in order to perform the prayer in its prescribed fixed time. You are not allowed to delay Ghusl until after sunrise, while you are able to perform it. If you are sick and making Ghusl during the night is harmful to you, you are required to perform Tayammum instead. Allaah The Almighty Says (what means): {But if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and wipe over your faces and hands with it.}[Quran 5: 6] 

When water is available but one is unable to use it, it is as if water is unavailable in principle.

We alert that one has to be certain or most likely believe that using water is harmful to him/her. If s/he only suspects or thinks that harm is possible, this is not enough.