Al-Baqarah 2:185 شهر رمضان الذي انزل فيه القران هدى للناس وبينات من الهدى والفرقان فمن شهد منكم الشهر فليصمه ومن كان مريضا او على سفر فعدة من ايام اخر يريد الله بكم اليسر ولا يريد بكم العسر ولتكملوا العدة ولتكبروا الله على ما هداكم ولعلكم تشكرون ١٨٥

The month of Ramadan in which was revealed the Qur’ân, a guidance for mankind and clear proofs for the guidance and the criterion (between right and wrong). So whoever of you sights (the crescent on the first night of) the month (of Ramadan i.e. is present at his home), he must observe Saum (fasts) that month, and whoever is ill or on a journey, the same number [of days which one did not observe Saum (fasts) must be made up] from other days. Allâh intends for you ease, and He does not want to make things difficult for you. (He wants that you) must complete the same number (of days), and that you must magnify Allâh [i.e. to say Takbîr (Allâhu Akbar; Allâh is the Most Great] for having guided you so that you may be grateful to Him.¹