It is reported that once, some good food was served to Anas [Ibn Mâlik] – Allâh be pleased with him, and [the person who served the food] was well off enough to afford good food. As he was eating, he kept a morsel of the food in his mouth for a while, then looked at the people and began to cry. Then he said, “By Allâh, I have accompanied people who, if they could get hold of this kind of food, would have fasted even more often, and spent less time not fasting. One of them would find only milk mixed with water [as food], which he would drink and then fast on.”
Al-Mu’âfâ b. ‘Imrân, Kitâb Al-Zuhd article 215.