Fasting is an obligatory law prescribed by Allah and an important part of Islam. Almighty Allah describes several verses about Fasting. Allah says
يٰٓـاَيُّهَا الَّذِيۡنَ اٰمَنُوۡا كُتِبَ عَلَيۡکُمُ الصِّيَامُ کَمَا كُتِبَ عَلَى الَّذِيۡنَ مِنۡ قَبۡلِکُمۡ لَعَلَّكُمۡ تَتَّقُوۡنَۙ
O believers, fasting is enjoined on you as it was on those before you, so that you might become righteous.
اَيَّامًا مَّعۡدُوۡدٰتٍؕ فَمَنۡ كَانَ مِنۡكُمۡ مَّرِيۡضًا اَوۡ عَلٰى سَفَرٍ فَعِدَّةٌ مِّنۡ اَيَّامٍ اُخَرَؕ وَعَلَى الَّذِيۡنَ يُطِيۡقُوۡنَهٗ فِدۡيَةٌ طَعَامُ مِسۡكِيۡنٍؕ فَمَنۡ تَطَوَّعَ خَيۡرًا فَهُوَ خَيۡرٌ لَّهٗ ؕ وَاَنۡ تَصُوۡمُوۡا خَيۡرٌ لَّـکُمۡ اِنۡ كُنۡتُمۡ تَعۡلَمُوۡنَ
Fast a (fixed) number of days, but if someone is ill or is travelling (he should complete) the number of days (he had missed); and those who find it hard to fast should expiate by feeding a poor person. For the good they do with a little hardship is better for men. And if you fast it is good for you, if you knew.
شَهۡرُ رَمَضَانَ الَّذِىۡٓ اُنۡزِلَ فِيۡهِ الۡقُرۡاٰنُ هُدًى لِّلنَّاسِ وَ بَيِّنٰتٍ مِّنَ الۡهُدٰى وَالۡفُرۡقَانِۚ فَمَنۡ شَهِدَ مِنۡكُمُ الشَّهۡرَ فَلۡيَـصُمۡهُ ؕ وَمَنۡ کَانَ مَرِيۡضًا اَوۡ عَلٰى سَفَرٍ فَعِدَّةٌ مِّنۡ اَيَّامٍ اُخَرَؕ يُرِيۡدُ اللّٰهُ بِکُمُ الۡيُسۡرَ وَلَا يُرِيۡدُ بِکُمُ الۡعُسۡرَ وَلِتُکۡمِلُوا الۡعِدَّةَ وَلِتُکَبِّرُوا اللّٰهَ عَلٰى مَا هَدٰٮكُمۡ وَلَعَلَّکُمۡ تَشۡكُرُوۡنَ
Ramadan is the month in which the Qur`an was revealed as guidance to man and clear proof of the guidance, and criterion (of falsehood and truth). So when you see the new moon you should fast the whole month; but a person who is ill or travelling (and fails to do so) should fast on other days, as God wishes ease and not hardship for you, so that you complete the (fixed) number (of fasts), and give glory to God for the guidance and be grateful.
اُحِلَّ لَـکُمۡ لَيۡلَةَ الصِّيَامِ الرَّفَثُ اِلٰى نِسَآئِكُمۡؕ هُنَّ لِبَاسٌ لَّـكُمۡ وَاَنۡـتُمۡ لِبَاسٌ لَّهُنَّ ؕ عَلِمَ اللّٰهُ اَنَّکُمۡ كُنۡتُمۡ تَخۡتَانُوۡنَ اَنۡفُسَکُمۡ فَتَابَ عَلَيۡكُمۡ وَعَفَا عَنۡكُمۡۚ فَالۡــئٰنَ بَاشِرُوۡهُنَّ وَابۡتَغُوۡا مَا کَتَبَ اللّٰهُ لَـكُمۡ وَكُلُوۡا وَاشۡرَبُوۡا حَتّٰى يَتَبَيَّنَ لَـكُمُ الۡخَـيۡطُ الۡاَبۡيَضُ مِنَ الۡخَـيۡطِ الۡاَسۡوَدِ مِنَ الۡفَجۡرِؕ ثُمَّ اَتِمُّوا الصِّيَامَ اِلَى الَّيۡلِۚ وَلَا تُبَاشِرُوۡهُنَّ وَاَنۡـتُمۡ عٰكِفُوۡنَ فِى الۡمَسٰجِدِؕ تِلۡكَ حُدُوۡدُ اللّٰهِ فَلَا تَقۡرَبُوۡهَا ؕ كَذٰلِكَ يُبَيِّنُ اللّٰهُ اٰيٰتِهٖ لِلنَّاسِ لَعَلَّهُمۡ يَتَّقُوۡنَ
You are allowed to sleep with your wives on the nights of the fast: They are your dress as you are theirs. God is aware you were cheating yourselves, so He turned to you and pardoned you. So now you may have intercourse with them, and seek what God has ordained for you. Eat and drink until the white thread of dawn appears clear from the dark line, then fast until the night falls; and abstain from your wives (when you have decided) to stay in the mosques for assiduous devotion. These are the bounds fixed by God, so keep well within them. So does God make His signs clear to men that they may take heed for themselves.