Allah singles out one act of worship and claims it for Himself: every deed of the son of Adam is for him, except fasting, it is Mine, and I shall reward it. Of all the worship multiplied by tens and hundreds, fasting alone is given a reward only Allah will measure.
Where this hadith comes from
This is a hadith qudsi: the Prophet (peace be upon him) is conveying Allah's own words, spoken in the first person ('Fasting is Mine, and I shall reward it'), yet these words are not part of the Qur'an. It is narrated by Abu Hurayrah (ra) and recorded by al-Bukhari (also by Muslim), graded sahih and agreed upon, so it stands on the soundest footing.
Notice what Allah does here. Of all the acts of worship, He singles out fasting and claims it for Himself, then keeps its reward in His own hand. Our concern is what this teaches the heart about sincerity and nearness to Allah, not the rules of when or how to fast, which belong to the scholars.
The key words
What it means, line by line
'Fasting is Mine, and it is I who reward it.' Every other deed has a known multiplier, but Allah leaves fasting's reward unnamed and takes it into His own hand. When the Most Generous keeps the figure to Himself, the reward is beyond what we could count.
'He gives up his desire, his food, and his drink for My sake.' This is the heart of it: a hidden surrender that only Allah can see, which is why fasting is almost pure sincerity. 'Fasting is a shield' that guards the soul, and the faster has 'two joys: a joy when he breaks his fast, and a joy when he meets his Lord,' the second far greater than the first.
The Qur'an names the inner aim of this worship: not hunger, but taqwa, a watchful awareness of Allah.
The worship no one can see
Why is fasting special? Because it is the most hidden of deeds. Prayer can be seen, charity can be seen, but fasting is invisible; a fasting person and a non-fasting one look exactly alike. Someone could claim to fast and break it in secret, and no one on earth would know. So fasting is almost pure sincerity by nature: there is no one to perform it for but Allah, which is why He claims it as His own.
A reward beyond measure
Other deeds have a stated multiplier; fasting's reward is left unspecified, given without measure, by Allah Himself. When the Generous keeps the reckoning of a deed to His own hand and does not even name the figure, you know the reward is beyond imagining. The patience of hunger, the restraint of the tongue, the surrender of a lawful pleasure for His sake, all of it is held by the One who misses nothing and repays without limit.
Carry this with you
Fasting is the secret worship Allah keeps for Himself.
Fasting is for Allah alone.
Of all deeds, He claims this one as His own and rewards it Himself.
It is pure by nature.
Invisible to others, there is no one to fast for but Allah, which makes it almost pure sincerity.
Its reward is unmeasured.
When the Generous keeps the reckoning to His own hand without naming the figure, the reward is beyond imagining.
Practice the hidden.
A voluntary fast, told to no one, trains the heart in worship that is wholly between you and Him.
A du'a to carry
رَبَّنَآ ءَاتِنَا فِى ٱلدُّنْيَا حَسَنَةً وَفِى ٱلْءَاخِرَةِ حَسَنَةً وَقِنَا عَذَابَ ٱلنَّارِ
Rabbana atina fid-dunya hasanatan wa fil-akhirati hasanatan wa qina 'adhab an-nar
Our Lord, give us in this world good and in the Hereafter good, and protect us from the punishment of the Fire. (Al-Baqarah 2:201)
A du'a of the fasting heart
Of all your worship, one act is so quietly sincere that Allah took it for His own and kept its reward a secret He will unveil Himself. There is something beautiful in worshipping where only He can see.
O Allah, accept our fasting, the seen and the hidden, and let it be purely for You. Reward us by Your own hand, and give us good in this world and the next, and save us from the Fire. Ameen.
The hadith qudsi is from sunnah.com: 'Fasting is Mine and it is I who give reward for it,' narrated by Abu Hurayrah (ra), recorded by al-Bukhari (also Muslim), graded sahih (agreed upon). The supporting Qur'an (2:201) is in Uthmani script verified via quran.ai (ar-uthmani-minimal) with the Saheeh International translation. Per the editorial policy this stays with the spiritual meaning (sincerity and the virtue of fasting), not the fiqh of fasting. FOR SCHOLAR REVIEW before publication.