Mishkat al-Masabih #1931

Anas said that in the course of a journey with the Prophet when some of them were fasting and others broke their fast, they alighted at a stage on a hot day, and while those who fasted collapsed those who had broken their fast rose and set up the tents and watered the riding-beasts, whereupon God's messenger said, “Those who broke their fast have earned all the reward today.” (Bukhari and Muslim.)