The Messenger of Allah (sal Allahu alaihi wa sallam) said: “Every good deed of the son of Adam will be multiplied between ten and seven hundred times, but Allah says, ‘Except for fasting, because it is for Me and I will give the reward for it.’” [Bukhaari]
Among the actions which will be multiplied beyond measure, to an extent known only to the One Who gives the reward, is fasting.
The reason that the one who fasts will be given reward without measure is that fasting requires Sabr (patience), and those who are patient will be given reward without measure. Allah (subhana wa ta’ala) says: “Only those who are patient shall receive their reward in full, without measure.” [Surah Az-Zumar: Ayat 10]
Imaam Qurtubi said: “The scholars said, ‘Every reward will be measured and weighed out, except (the reward for) fasting, which will be poured out and heaped up.’” [Tafseer al-Qurtubi]
