Reward for fasting is up to Allah and its several other virtues

the Messenger of Allah ﷺ said, "Allah said, 'All the deeds of Adam's sons (people) are for them, except fasting which is for Me, and I will give the reward for it.'

"Fasting is a shield (protection from the Hellfire and from committing sins). If one of you is fasting, he should avoid sexual relation with his wife and quarreling, and if somebody should fight or quarrel with him, he should say: I am fasting."

"By Him in Whose Hands my soul is, the unpleasant smell coming out from the mouth of a fasting person is better in the sight of Allah than the smell of musk."

"There are two pleasures for the fasting person, one at the time of breaking his fast, and the other at the time when he will meet his Lord; then he will be pleased because of his fasting."  

قَالَ رَسُولُ اللَّهِ ﷺ: «قَالَ اللَّهُ: كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلاَّ الصِّيَامَ، فَإِنَّهُ لِي وَأَنَا أَجْزِي بِهِ۔»

«وَالصِّيَامُ جُنَّةٌ وَإِذَا كَانَ يَوْمُ صَوْمِ أَحَدِكُمْ فَلاَ يَرْفُثْ وَلاَ يَصْخَبْ فَإِنْ سَابَّهُ أَحَدٌ أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي امْرُؤٌ صَائِمٌ۔»

«وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ، لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ مِنْ رِيحِ الْمِسْكِ لِلصَّائِمِ۔»

«فَرْحَتَانِ يَفْرَحُهُمَا إِذَا أَفْطَرَ فَرِحَ وَإِذَا لَقِيَ رَبَّهُ فَرِحَ بِصَوْمِهِ۔»  

Allah the Exalted and Majestic said: Every act of the son of Adam is for him, except fasting. It is (exclusively) meant for Me and I (alone) will reward it. Fasting is a shield. When any one of you is fasting on a day, he should neither indulge in obscene language, nor raise the voice; or if anyone reviles him or tries to quarrel with him he should say: I am a person fasting. By Him, in Whose Hand is the life of Muhammad, the breath of the observer of fast is sweeter to Allah on the Day of judgment than the fragrance of musk. The one who fasts has two (occasions) of joy, one when he breaks the fast he is glad with the breaking of (the fast) and one when he meets his Lord he is glad with his fast.  

أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ ؓ يَقُولُ قَالَ رَسُولُ اللَّهِ ﷺ قَالَ اللَّهُ ﷻ كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلاَّ الصِّيَامَ فَإِنَّهُ لِي وَأَنَا أَجْزِي بِهِ وَالصِّيَامُ جُنَّةٌ فَإِذَا كَانَ يَوْمُ صَوْمِ أَحَدِكُمْ فَلاَ يَرْفُثْ يَوْمَئِذٍ وَلاَ يَسْخَبْ فَإِنْ سَابَّهُ أَحَدٌ أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي امْرُؤٌ صَائِمٌ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ يَوْمَ الْقِيَامَةِ مِنْ رِيحِ الْمِسْكِ وَلِلصَّائِمِ فَرْحَتَانِ يَفْرَحُهُمَا إِذَا أَفْطَرَ فَرِحَ بِفِطْرِهِ وَإِذَا لَقِيَ رَبَّهُ فَرِحَ بِصَوْمِهِ  

"The Messenger of Allah said: '(Allah says) Every deed of the son of Adam is for him, except fasting; it is for me and I shall reward for it. Fasting is a shield. If any one of you is fasting, let him no utter obscene talk or raise his voice in anger, and if anyone insults him or wants to fight, let him say: I am fasting. By the One in whose hand is the soul of Muhammad, the smell coming from the mouth of the fasting person is better before Allah than the fragrance of musk. The fasting person has two moments of joy: When he breaks his fast he rejoices at breaking his fast and when he meets his Lord, the Mighty and Sublime, he will rejoice at having fasted." '  

قَالَ رَسُولُ اللَّهِ ﷺ كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلاَّ الصِّيَامَ هُوَ لِي وَأَنَا أَجْزِي بِهِ وَالصِّيَامُ جُنَّةٌ إِذَا كَانَ يَوْمُ صِيَامِ أَحَدِكُمْ فَلاَ يَرْفُثْ وَلاَ يَصْخَبْ فَإِنْ شَاتَمَهُ أَحَدٌ أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي صَائِمٌ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ يَوْمَ الْقِيَامَةِ مِنْ رِيحِ الْمِسْكِ لِلصَّائِمِ فَرْحَتَانِ يَفْرَحُهُمَا إِذَا أَفْطَرَ فَرِحَ بِفِطْرِهِ وَإِذَا لَقِيَ رَبَّهُ ﷻ فَرِحَ بِصَوْمِهِ  

"The Messenger of Allah said: 'Allah, the Mighty and sublime, said: Every deed of the son of Adam is for him, except fasting; it is for me and I shall reward for it. Fasting is a shield. If any one of you is observing a fast, let him not utte obscene a fast, let him not utter obscene talk or raise his voice in anger, and if anyone insults him or wants to fight, let him say: I am a person who is fasting. By the One in Whose hand is the soul of Muhammad, the smell coming from the mouth of the fasting person is better before Allah than the fragrance of musk." ' (Sahih) This Hadith was narrated from Abu Hurairah by Saeed bin Al-Musayyab.  

قَالَ رَسُولُ اللَّهِ ﷺ قَالَ اللَّهُ ﷻ كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلاَّ الصِّيَامَ هُوَ لِي وَأَنَا أَجْزِي بِهِ الصِّيَامُ جُنَّةٌ فَإِذَا كَانَ يَوْمُ صَوْمِ أَحَدِكُمْ فَلاَ يَرْفُثْ وَلاَ يَصْخَبْ فَإِنْ شَاتَمَهُ أَحَدٌ أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي امْرُؤٌ صَائِمٌ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ مِنْ رِيحِ الْمِسْكِ وَقَدْ رَوَى هَذَا الْحَدِيثَ عَنْ أَبِي هُرَيْرَةَ سَعِيدُ بْنُ الْمُسَيَّبِ  

"The Messenger of Allah said: '(Allah says) Every deed of the son of Adam is for him, except fasting; it is for me and I shall reward for it. Fasting is a shield. If any one of you is fasting, let him no utter obscene talk or raise his voice in anger, and if anyone insults him or wants to fight, let him say: I am fasting. By the One in whose hand is the soul of Muhammad, the smell coming from the mouth of the fasting person is better before Allah than the fragrance of musk. The fasting person has two moments of joy: When he breaks his fast he rejoices at breaking his fast and when he meets his Lord, the Mighty and Sublime, he will rejoice at having fasted." ' (Using translation from Nasāʾī 2216)  

قَالَ رَسُولُ اللهِ ﷺ كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلَّا الصِّيَامَ فَإِنَّهُ لِي وَأَنَا أَجْزِي بِهِ وَالصِّيَامُ جُنَّةٌ وَإِذَا كَانَ يَوْمُ صَوْمِ أَحَدِكُمْ فَلَا يَرْفُثْ يَوْمَئِذٍ وَلَا يَصْخَبْ فَإِنْ سَابَّهُ أَحَدٌ أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي امْرُؤٌ صَائِمٌ مَرَّتَيْنِ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللهِ يَوْمَ الْقِيَامَةِ مِنْ رِيحِ الْمِسْكِ وَلِلصَّائِمِ فَرْحَتَانِ يَفْرَحُهُمَا إِذَا أَفْطَرَ فَرِحَ بِفِطْرِهِ وَإِذَا لَقِيَ رَبَّهُ ﷻ فَرِحَ بِصِيَامِهِ  

the Messenger of Allah ﷺ said, "Allah said, 'All the deeds of Adam's sons (people) are for them, except fasting which is for Me, and I will give the reward for it.'

"Fasting is a shield or protection from the fire and from committing sins. If one of you is fasting, he should avoid sexual relation with his wife and quarreling, and if somebody should fight or quarrel with him, he should say: I am fasting."

"By Him in Whose Hands my soul is, the unpleasant smell coming out from the mouth of a fasting person is better in the sight of Allah than the smell of musk."

"There are two pleasures for the fasting person, one at the time of breaking his fast, and the other at the time when he will meet his Lord; then he will be pleased because of his fasting." (Using translation from Bukhārī 1904)  

قَالَ رَسُولُ اللهِ ﷺ قَالَ اللهُ كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلَّا الصِّيَامَ هُوَ لِي وَأَنَا أَجْزِي بِهِ وَالصِّيَامُ جُنَّةٌ إِذَا كَانَ يَوْمُ صِيَامِ أَحَدِكُمْ فَلَا يَرْفُثْ وَلَا يَصْخَبْ فَإِنْ شَاتَمَهُ أَحَدٌ أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي صَائِمٌ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللهِ يَوْمَ الْقِيَامَةِ مِنْ رِيحِ الْمِسْكِ لِلصَّائِمِ فَرْحَتَانِ يَفْرَحُهُمَا إِذَا أَفْطَرَ فَرِحَ بِفِطْرِهِ وَإِذَا لَقِيَ رَبَّهُ فَرِحَ بِصَوْمِهِ  

"قَال الله - ﷻ - كُل عَمَلَ ابْنِ آدَمَ لَهُ إِلا الصِّيَامُ فإِنهُ لِي وأنَا أجْزِى بِهِ، وَالصّيَامُ جُنةٌ، وإذا كَانَ يَوْم صَوْم أحَدكُم فَلَا يَرفثْ، وَلَا يَصخَبْ وإنْ سَابَهُ أحَدٌ أوُ قَاتَلَهُ فَليَقُلْ: إِنّى امرُؤ صَائِم، والذِى نَفْس محمد بيَدِهِ لَخُلوفُ فَم الصائِم أطيَبُ عِنْدَ اللهِ مِنْ رِيح المِسْكِ، ولِلصّائِم فَرحَتَان يَفْرَحُهمَا: إِذَا أَفْطَرَ فَرِحَ بِفِطرِه، وإِذَا لَقِيَ ربَهُ فَرِحَ بصَوْمِهِ".