He seems to be a devout muslim, rather than asking him to change his attire it would be better if we analyze the situation in this way. Doha is a place where people from all walks of life come together and work. If this person comes in the attire as u have mentioned, it will definately change the image of the company, - this only adds to show that the company has a multi- cultural work enviroment, where people from diverse backgrounds work together. Plz donot get me wrong , think calmly, if he was in the same attire during his interiew and also been selected, then u should think that neither the HR nor the Management has any problem with this. If u tell him now ur company is at fault by not mentioning the company's attire before.As far as the work is good this should not be point of major concern for you. but surely your boss has a problem,- Firstly because he is not interferring in the whole issue and asking you to talk. If you mention this to that person, I am sure i will give the resignation but will not accept to change his attire,

Many people here can be seen , even the directors of major firms like Qataris can be seen in this attire, If you ask him anything about the beard, your boss is inviting trouble because if he happens to go to wakf board regarding the whole issue your company will be in trouble and blacklisted in Qatar.

I only wanted to elobrate clerarly on this issue, nothing personal

regards
live and let live