Verse of the Holy Quran 

شَهْرُ رَمَضَانَ الَّذِي اُنْزِلَ فِيهِ الْقُرْاٰنُ هُدًى لِلنَّاسِ وَبَيِّنَاتٍ مِنَ الْهُدٰى وَالْفُرْقَانِۚ فَمَنْ شَهِدَ مِنْكُمُ الشَّهْرَ فَلْيَصُمْهُ وَمَنْ كَانَ مَرِيضًا اَوْ عَلٰى سَفَرٍ فَعِدَّةٌ مِنْ اَيَّامٍ اُخَرَ يُرِيدُ اللّٰهُ بِكُمُ الْيُسْرَ وَلَا يُرِيدُ بِكُمُ
الْعُسْرَ وَلِتُكْمِلُوا الْعِدَّةَ وَلِتُكَبِّرُوا اللّٰهَ عَلٰى مَا هَدٰيكُمْ وَلَعَلَّكُمْ تَشْكُرُونَ

It is the month of Ramadan in which the Quran was sent down, which is a guide to guidance and evidence to distinguish right from wrong, to guide people. Therefore, whoever of you witnesses this month should fast during it. And whoever is sick or on a journey, let him make up for it on the other days in the same number of days that he cannot catch up. Allah desires ease for you and does not desire hardship for you. He wants you to complete the number and praise Allah for showing you the right path. I hope you will be thankful.
(Bakara 185)