The Prophet (s) said, “The strong believer is better and more beloved to Allah than the weak believer, while there is good in both.”
See: IslamicWorkplace. Healthy body, healthy mind, healthy spirit.
To keep the body in good health is a duty… otherwise we shall not be able to keep our mind strong and clear.
Here are some more quotes for healthy living: http://summertomato.com/great-thinkers-10-inspiring-quotes-for-healthy-living/ .