When the Previous Rebbe's grandmother, Rebbetzin Rivkah, was eighteen, she fell ill and the physician ordered her to eat immediately upon awakening. She, however, did not wish to eat before davening, so she davened very early, then ate breakfast. When her father-in-law, the Tzemach Tzedek, learned of this he said to her: "A Jew must be healthy and strong. Regarding mitzvos, the Torah says: 'Live in them,' meaning, one should bring vitality into his performance of the mitzvos. To be able to infuse mitzvos with vitality, one must be strong and joyful." He then concluded: "You should not be without food. Better to eat for the sake of davening than to daven for the sake of eating." He then blessed her with long life.

HaYom Yom, entry for 10 Shvat