(God’s System: Twelve Months Per Year*)
The count of months, as far as God is concerned, is twelve.* This has been God’s law, since the day He created the heavens and the earth. Four of them are sacred. This is the perfect religion; you shall not wrong your souls (by fighting) during the Sacred Months. However, you may declare all-out war against the idol worshipers (even during the Sacred Months), when they declare all-out war against you, and know that God is on the side of the righteous.
إِنَّ عِدَّةَ الشُّهورِ عِندَ اللَّهِ اثنا عَشَرَ شَهرًا فى كِتٰبِ اللَّهِ يَومَ خَلَقَ السَّمٰوٰتِ وَالأَرضَ مِنها أَربَعَةٌ حُرُمٌ ذٰلِكَ الدّينُ القَيِّمُ فَلا تَظلِموا فيهِنَّ أَنفُسَكُم وَقٰتِلُوا المُشرِكينَ كافَّةً كَما يُقٰتِلونَكُم كافَّةً وَاعلَموا أَنَّ اللَّهَ مَعَ المُتَّقينَ
inna ‘iddatash shuhoori ‘indal laahis naa ‘ashara shahran fee Kitaabil laahi yawma khalaqas samaawaati wal arda minhaaa arba’atun hurum; zaalikad deenul qaiyim; falaa tazlimoo feehinna anfusakum; wa qaatilul mushrikeena kaaaffatan kamaa yuqaati loonakum kaaaffah; wa’lamooo annal laaha ma’al muttaqeen
*9:36 The word “month” is mentioned in the Quran 12 times, and “day” 365 times.