﴿شَهرُ رَمَضانَ الَّذي أُنزِلَ فيهِ القُرآنُ هُدًى لِلنّاسِ وَبَيِّناتٍ مِنَ الهُدى وَالفُرقانِ فَمَن شَهِدَ مِنكُمُ الشَّهرَ فَليَصُمهُ وَمَن كانَ مَريضًا أَو عَلى سَفَرٍ فَعِدَّةٌ مِن أَيّامٍ أُخَرَ يُريدُ اللَّهُ بِكُمُ اليُسرَ وَلا يُريدُ بِكُمُ العُسرَ وَلِتُكمِلُوا العِدَّةَ وَلِتُكَبِّرُوا اللَّهَ عَلى ما هَداكُم وَلَعَلَّكُم تَشكُرونَ﴾
[لبقرة: ١٨٥]

The month of Ramadān [is that] in which was revealed the Qur’ān, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the crescent of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days. Allāh intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allāh for that [to] which He has guided you; and perhaps you will be grateful. Also, "whoever is present during the month."
[Al-Baqarah: 185]