بسم الله الرحمن الرحيم
(Fatwa: 731/746/N=07/1437)
If you may be granted causal leave as per the rules and regulations then you should go for Hajj on causal leave only. No matter in such a case you do not get the salary of all or some days as it is not lawful to get fake medical certificate while one is not sick. It is lie, deceit and treachery which in no way is allowed in Islam.
عن أبي هريرة رضي الله عنه قال أن رسول الله صلى الله عليه وسلم قال: “من غشنا فليس منا” (صحيح مسلم شريف 1:70، مطبوعه : مكتبه اشرفيه ديوبند).
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband