Answered by Shaykh Faraz Rabbani
Washing the hair under the beard/eyebrows is fard in a ghusl, as opposed to wudu (am I right?)
I never used to think too much about this, but now my beard has become quitethick and I am not 100% sure that water always went to the skin. I usuallyscrub my beard, but cannot be certain that water went through (though itprobably did). Do I have to redo my prayers? How can one become certain that water has gotten through, as I cannot see under my beard in a mirror? Is there a particular way to wash the beard?
Also, in a ghusl, water has to get through to the skin under the eyebrows, as opposed to wudu (is that right?). How can one be certain that water has gotten through? If I wash my face in the normal way that most people do without rubbing my eyebrows with my fingers separately, is that enough? Further, there is no mention of the above in Behiste Zewar, Imdad ul-Fiqh or Ta’lim ul-Haq. Is there a difference of opinion about this?
The initial presumption for acts is that they are valid, unless you become certain that they are not. As such, your past purificatory baths (ghuls) would be considered valid, as you have no certain proof that they were not.
Water has to reach all the outward skin of the body, even if covered by hair, in ghusl. No one has said that we need to examine our skin with a microscope or to look in a mirror; rather, we wash until it would be reasonably assumed that the water did in fact go through.
[Shaykh Abu Usamah notes: You should wash your body in such a way that water will reach every part. Obviously you cannot be certain that the water has reached certain areas that you cannot see. However after you have washed it in a manner that water will probably reach there you must be satisfied and not allow doubts to plague you.