Chapter 2, Verse 185, The Cow
سُوۡرَةُ البَقَرَة
شَهۡرُ رَمَضَانَ ٱلَّذِيٓ أُنزِلَ فِيهِ ٱلۡقُرۡءَانُ هُدٗى لِّلنَّاسِ وَبَيِّنَٰتٖ مِّنَ ٱلۡهُدَىٰ وَٱلۡفُرۡقَانِۚ فَمَن شَهِدَ مِنكُمُ ٱلشَّهۡرَ فَلۡيَصُمۡهُۖ وَمَن كَانَ مَرِيضًا أَوۡ عَلَىٰ سَفَرٖ فَعِدَّةٞ مِّنۡ أَيَّامٍ أُخَرَۗ يُرِيدُ ٱللَّهُ بِكُمُ ٱلۡيُسۡرَ وَلَا يُرِيدُ بِكُمُ ٱلۡعُسۡرَ وَلِتُكۡمِلُواْ ٱلۡعِدَّةَ وَلِتُكَبِّرُواْ ٱللَّهَ عَلَىٰ مَا هَدَىٰكُمۡ وَلَعَلَّكُمۡ تَشۡكُرُونَ
The month of Ramadan in which was revealed the Quran, 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. Allah 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 Allah [i.e. to say Takbir (Allahu-Akbar; Allah is the Most Great) on seeing the crescent of the months of Ramadan and Shawwal] for having guided you so that you may be grateful to Him.
Chapter 9, Verse 36, Repentance
سورة التوبة
إِنَّ عِدَّةَ ٱلشُّهُورِ عِندَ ٱللَّهِ ٱثۡنَا عَشَرَ شَهۡرٗا فِي كِتَٰبِ ٱللَّهِ يَوۡمَ خَلَقَ ٱلسَّمَٰوَٰتِ وَٱلۡأَرۡضَ مِنۡهَآ أَرۡبَعَةٌ حُرُمٞۚ ذَٰلِكَ ٱلدِّينُ ٱلۡقَيِّمُۚ فَلَا تَظۡلِمُواْ فِيهِنَّ أَنفُسَكُمۡۚ وَقَٰتِلُواْ ٱلۡمُشۡرِكِينَ كَآفَّةٗ كَمَا يُقَٰتِلُونَكُمۡ كَآفَّةٗۚ وَٱعۡلَمُوٓاْ أَنَّ ٱللَّهَ مَعَ ٱلۡمُتَّقِينَ
Verily, the number of months with Allah is twelve months (in a year), so was it ordained by Allah on the Day when He created the heavens and the earth; of them four are Sacred, (i.e. the 1st, the 7th, the 11th and the 12th months of the Islamic calendar). That is the right religion, so wrong not yourselves therein, and fight against the Mushrikun (polytheists, pagans, idolaters, disbelievers in the Oneness of Allah) collectively, as they fight against you collectively. But know that Allah is with those who are Al-Muttaqun (the pious - see V. 2:2).
Chapter 9, Verse 37, Repentance
سورة التوبة
إِنَّمَا ٱلنَّسِيٓءُ زِيَادَةٞ فِي ٱلۡكُفۡرِۖ يُضَلُّ بِهِ ٱلَّذِينَ كَفَرُواْ يُحِلُّونَهُۥ عَامٗا وَيُحَرِّمُونَهُۥ عَامٗا لِّيُوَاطِـُٔواْ عِدَّةَ مَا حَرَّمَ ٱللَّهُ فَيُحِلُّواْ مَا حَرَّمَ ٱللَّهُۚ زُيِّنَ لَهُمۡ سُوٓءُ أَعۡمَٰلِهِمۡۗ وَٱللَّهُ لَا يَهۡدِي ٱلۡقَوۡمَ ٱلۡكَٰفِرِينَ
The postponing (of a Sacred Month) is indeed an addition to disbelief: thereby the disbelievers are led astray, for they make it lawful one year and forbid it another year in order to adjust the number of months forbidden by Allah, and make such forbidden ones lawful. The evil of their deeds seems pleasing to them. And Allah guides not the people, who disbelieve.
