The reward for fasting is more than seven hundredfold

Praise be to Allah

It is proven in the hadith that Abu Hurayrah (may Allah be pleased with
him) said: The Messenger of Allah (blessings and peace of Allah be upon
him) said: “Every deed of the son of Adam will be multiplied between ten
and seven hundred times. Allah, may He be glorified and exalted, said:
Except fasting. It is for Me and I shall reward for it. He gives up his
desires and his food for My sake.”

Narrated by Muslim (1151) 

In
their commentaries on this hadith, the scholars stated that what this means
is that the reward for fasting is multiplied more than seven hundredfold. We
will quote here some of their many comments: 

Abu’l-Waleed al-Baaji (d. 474 AH – may Allah have mercy on him) said: 

The virtue of the multiple reward for fasting is that Allah attributed it to
Himself, may He be exalted. This implies that it will be more than seven
hundredfold.

End quote from al-Muntaqa Sharh al-Muwatta’ (2/74) 

Abu Haamid al-Ghazaali (d. 505 AH – may Allah have mercy on him) said: 

Allah, may He be exalted, says (interpretation of the meaning):
“Only
those who are patient shall receive their rewards in full, without reckoning”
[az-Zumar 39:10].
Fasting is half of patience, so its reward is beyond what one might estimate
and give a figure for.

End quote from Ihya’ ‘Uloom ad-Deen (1/231) 

Ibn al-‘Arabi (d. 543 AH – may Allah have mercy on him) said:

Our Lord, may He be Blessed and exalted, has told us that the reward for
righteous deeds may be multiplied by a factor between one and seven hundred,
but He has withheld from us knowledge of the amount of the reward for
patience and has kept knowledge thereof to Himself.
“Only
those who are patient shall receive their rewards in full, without reckoning”
[az-Zumar 39:10].
Because fasting is a type of patience, as the one who fasts refrains from
physical desires, Allah, may He be exalted, said: “Every deed of the son of
Adam is for him, except fasting; it is for Me and I shall reward for it.”
The scholars said: The reward (of every deed) will be weighed out and
measured out, except the reward for fasting; it will be scooped up by the
handful. Hence Maalik said: It is patience in bearing the calamities and
sorrows of this world, so undoubtedly everyone who delegates his affairs to
Allah, bears patiently whatever befalls him, and refrains from whatever is
forbidden to him, his reward cannot be estimated. The lawgiver indicated
that fasting comes under this category of patience.

end quote from Ahkaam al-Qur’an (4/77) 

al-Qaadi ‘Iyaad (d. 544 AH – may Allah have mercy on him) said: 

Moreover, Allah bestows upon whomever He wills whatever He wills of increase
up to seven hundredfold, and even beyond that, such as cannot be estimated,
as He, may He be exalted, says (interpretation of the meaning):
“Only
those who are patient shall receive their rewards in full, without reckoning”
[az-Zumar 39:10]. And He
said: Except for fasting, for it is for Me and I shall reward for it” after
mentioning the seven hundredfold reward for it.

End quote from Ikmaal al-Mu‘allim bi Fawaa’id Muslim (8/184). 

Ibn Rajab (d. 795 AH – may Allah have mercy on him) said: 

According to the first report [i.e., that is mentioned at the beginning of
the answer], the exception of fasting from the deeds that receive a multiple
reward means that all good deeds receive a tenfold reward, up to seven
hundredfold, except fasting, for the multiplication of its reward is not
limited to that; rather Allah, may He be blessed and exalted, may multiply
it greatly, without limiting the number. For fasting is a kind of patience,
and Allah, may He be exalted, says (interpretation of the meaning):
“Only
those who are patient shall receive their rewards in full, without reckoning”
[az-Zumar 39:10]. Hence
it was narrated from the Prophet (blessings and peace of Allah be upon him)
that he called Ramadan the month of patience. 

According to another hadith, the Prophet (blessings and peace of Allah be
upon him) said: “Fasting is half of patience.” Narrated by at-Tirmidhi. 

Patience is of three types: patience in obeying Allah, patience in
refraining from that which Allah has prohibited, and patience in accepting
the decree of Allah when it is hurtful. All three types of patience are
combined in fasting. 

End quote from Lataa’if al-Ma‘aarif by Ibn Rajab (p. 150) 

Ibn al-Mulaqqin (d. 804 AH – may Allah have mercy on him) said: 

It
was said the concerning the verse in which Allah, may He be exalted, says
(interpretation of the meaning), “No
person knows what is kept hidden for them of joy as a reward for what they
used to do” [as-Sajdah
32:17] that “what
they used to do” was fasting, so they will be rewarded abundantly,
without measure. Fasting is singled out for the more than seven hundredfold
reward in this hadith.

End quote from at-Tawdeeh li Sharh al-Jaami‘ as-Saheeh (13/28) 

Shaykh as-Sa‘di (d. 1376 – may Allah have mercy on him) said: 

An
exception is made in this hadith for fasting, which Allah says is for Him,
and that He is the One Who will reward for it, on the basis of His
generosity and kindness, without meaning that the multiple reward for their
fasting is like the reward for other deeds. This is something that cannot be
expressed; rather He will reward them with that which no eye has seen, no
ear has heard, nor has it ever crossed the mind of man. This hadith points
out the reason for singling out this reward for fasting, and tells us that
the fasting person gives up the desires of his nafs that he is naturally
inclined to love and to give precedence to over other things, and that are
also necessary for him, but the fasting person gives precedence to love of
his Lord over these things, so he gives them up in a manner that no one
could know about except Allah, so his love for Allah becomes more important
and overwhelms any other natural inclinations, and seeking the pleasure of
his Lord takes precedence over attaining his own whims and desires.
Therefore Allah singles out fasting as being for Him and has promised that
the reward for fasting is with Him. So what do you think of the reward that
the Most Gracious, the Most Merciful, the Most Generous, the Bestower of
blessings – Whose generosity encompasses all that exists, and He has singled
out His close friends for the greatest share of His generosity, and has
decreed for them and made available to them the means by which they may
attain what He has of reward in a manner that could not cross the mind of
any person – how do you think that Allah will reward these sincere fasting
people? 

Here the pen must stop (for I have made my point). Joy will fill the heart
of the fasting person for having done an act that Allah has said is for Him,
and has made its reward commensurate with His generosity and kindness. That
is the grace of Allah that he bestows upon whomever He will, and Allah is
the Possessor of great bounty.

End quote from Bahjat Quloob al-Abraar (p. 94-95) 

Shaykh Ibn ‘Uthaymeen (d. 1421 AH – may Allah have mercy on him) said:

 The reward for acts of worship is tenfold up to seven hundredfold, up to
many times more, except fasting, for it is Allah Who will reward for it.
What that means is that the reward for it is very great indeed. The scholars
said that this is because fasting combines three types of patience, namely
patience in obeying Allah, patience in refraining from disobeying Allah, and
patience in accepting His decree. It is patience in obeying Allah because
the individual is patient in doing this act of obedience. It is patience in
refraining from disobeying Him because he avoids that which is prohibited
for the fasting person. And it is patience in accepting the decree of Allah
because the fasting person experiences the pain of thirst, hunger, tiredness
and lack of energy. Hence fasting is one of the most sublime forms of
patience, because it combines the three types of patience, and Allah, may He
be exalted, says (interpretation of the meaning): “Only
those who are patient shall receive their rewards in full, without reckoning”
[az-Zumar 39:10]. 

End quote from ash-Sharh al-Mumti‘ (6/458) 

And Allah knows best.