Sahih Bukhari, Chapter: Jihaad (Fighting for the cause of Allah)

We were with the Prophet (SAW) (on a journey) and the only shade one could have was the shade made by one's own garment. Those who observed saum (fast) did not do any work and those who did not fast served the camels and brought the water on them and treated the sick and (wounded). So, the Prophet (SAW) said, "Today, those who were not fasting took (all) the reward."