Why did Allah Almighty specify the reward for fasting to be given by Him alone?

Allah the Almighty glorifies fasting above all other acts of worship in several ways, the most important of which are:

1. Sincerity of Worship: Fasting is a secret act of worship known only to Allah, which reduces the likelihood of showing off. 2. Reward Without Measure: Allah alone knows the extent of the reward for fasting and the multiplication of its good deeds without limit, whereas other deeds are rewarded from tenfold to seven hundredfold, as stated in His saying: ﴿Indeed, the patient will be given their reward without account.﴾ 3. Love and Preference: Attributing fasting to Allah with "fasting is for Me" signifies that it is the most beloved and preferred act of worship to Him. The Messenger of Allah, peace and blessings be upon him, said: "You must fast, for there is nothing like it." 4. Honor and Glorification: Attributing fasting to Allah is an attribution of honor and glorification, just as it is said "the House of Allah."

Fasting is patience in obeying Allah, patience in abstaining from His prohibitions, and patience in enduring Allah's painful decrees. Thus, it combines the three types of patience, and the fasting person deserves a reward without measure.