إِنَّ عِدَّةَ ٱلشُّهُورِ عِندَ ٱللَّهِ ٱثْنَا عَشَرَ شَهْرًا فِى كِتَٰبِ ٱللَّهِ يَوْمَ خَلَقَ ٱلسَّمَٰوَٰتِ وَٱلْأَرْضَ مِنْهَآ أَرْبَعَةٌ حُرُمٌ ۚ ذَٰلِكَ ٱلدِّينُ ٱلْقَيِّمُ ۚ فَلَا تَظْلِمُوا۟ فِيهِنَّ أَنفُسَكُمْ ۚ وَقَٰتِلُوا۟ ٱلْمُشْرِكِينَ كَآفَّةً كَمَا يُقَٰتِلُونَكُمْ كَآفَّةً ۚ وَٱعْلَمُوٓا۟ أَنَّ ٱللَّهَ مَعَ ٱلْمُتَّقِينَ
Important Words:
کتاب (ordinance) is derived from کتب i.e. (1) he wrote; (2) he prescribed or ordained. کتاب means, a book or a writing; Divine prescript or ordinance or decree (Lane). See also 2:54 & 2:130.
Commentary:
The words فی کتاب اللّٰه (by Allah’s ordinance) mean that God so ordained on the day when He created the heavens and the earth that the number of months should be twelve, i.e. the law of nature determines that number, which holds true both in the solar and the lunar system.
The four sacred months are Dhul-Qa‘dah, Dhul-Hijjah, Muharram, and Rajab. These months have been held sacred by the Arabs, who are mostly descended from Abraham, from time immemorial and Islam confirmed their sacredness. It is considered unlawful to wage war or, for that matter, to continue a state of war in these four months unless, as the Quran points out, the enemy is the first to violate their sanctity. See also note on 2:218.
Both the lunar and the solar years comprise 12 months.
The four Sacred Months are Dhul-Qa‘dah, Dhul-Hijjah, Muharram and Rajab.