Q: Can I get sawab (reward) in going to the gym getting my body in shape for my future wife? (text)
A: Allah (SWT) rewards a man for looking his best for his family. We agree, it not only for a woman to look her best, men too must place some effort into the matter. Allah has given us all a body as part of Amanah (trust.) This trust demands that we eat healthy and place into our bodies that which benefits our physical and spiritual health. Good health also requires exercise to the extent that the gym or area of exercise does not become our second home.
Make your intention as follows: Oh Allah i am seeking better health to better remember you and can be of better service and more appealing to Your creation so as to aid your creation to all types of good. Ameen
Go and exercise when the opposite gender is not present. Guard your eyes and refrain from looking at what Allah has made forbidden for you to look at. Your going to the gym is due to an alternative not existing for you at your home, gym at your apartment complex, work, etc.
You must be in an environment that does not entice you to advance in any added wrongs.
Allah Certainly Knows Best.