Do the rewards for fasting multiply by more than seven hundredfold, due to Allah Almighty's saying: "Fasting is for Me, and I shall reward for it"?

Summary of the answer:

The reward for fasting is multiplied manyfold, exceeding seven hundred times, because it has been singled out from all other deeds by Allah's saying: "Except for fasting, for it is for Me, and I shall reward for it." This exception is interpreted to mean that the reward for fasting is not confined to a specific number, but rather given "without measure," due to the fact that fasting combines all three types of patience: patience in obedience, patience from disobedience, and patience in the face of painful decrees.