I just had a post removed from this thread which said he (your housemate) could go back to "IZLAPHOMIA!! !! !". I hope that was too stupid to be interpreted seriously, but apparently not.
So here is the rest of that post, without any silliness.
In your tenancy agreement, there should be a clause about 'quiet enjoyment' of the property, which means exactly what it says.
He s of course perfectly welcome to find a house where his praying is not only not considered a disruption, but is perfectly welcome to his fellow housemates.
Pointing out this clause in your contract should help no end with whatever authorities you must interact with.
There is no reason why someone with your disability should have to put up with that sort of thing.
It may be however that your landlord is a Muslim, in which case you are probably stuffed.
I trust that this post now passes the PC sensors and will be approved.