How can the Hadith, "Whoever fasts one day for the sake of Allah, Allah will distance his face from the Fire by seventy autumns," be reconciled with the Hadith, "Every deed of the son of Adam is for him, except fasting, for it is for Me and I shall reward for it"?

Fasting is an act purely for Allah Almighty, and He recompenses it without measure. The extent of its reward is known to none but Allah. This does not contradict Allah's disclosure of some of the virtues of fasting, such as: its distancing one from Hellfire by seventy autumns, and its being on the right side of the deceased in their grave, protecting them from torment. Thus, Allah Almighty's statement, "And I recompense it," indicates the greatness and abundance of the reward, because when the Generous Allah Himself undertakes the recompense, it signifies the immense value of the recompense and the vastness of the giving.