At-Taubah - 9:37

إِنَّمَا النَّسِيءُ زِيَادَةٌ فِي الْكُفْرِ يُضَلُّ بِهِ الَّذِينَ كَفَرُواْ يُحِلِّونَهُ عَامًا وَيُحَرِّمُونَهُ عَامًا لِّيُوَاطِؤُواْ عِدَّةَ مَا حَرَّمَ اللّهُ فَيُحِلُّواْ مَا حَرَّمَ اللّهُ زُيِّنَ لَهُمْ سُوءُ أَعْمَالِهِمْ وَاللّهُ لاَ يَهْدِي الْقَوْمَ الْكَافِرِينَ
[9:37]
Postponing (of the sacred month) is only an addition in unbelief, wherewith those who disbelieve are led astray, violating it one year and keeping it sacred another, that they may agree in the number (of months) that Allah has made sacred, and thus violate what Allah has made sacred; the evil of their doings is made fairseeming to them; and Allah does not guide the unbelieving people.
Verily the transposing (of a prohibited month) is an addition to Unbelief: the Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, in order to adjust the number of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah guideth not those who reject Faith.
Postponement (of a sacred month) is only an excess of disbelief whereby those who disbelieve are misled; they allow it one year and forbid it (another) year, that they may make up the number of the months which Allah hath hallowed, so that they allow that which Allah hath forbidden. The evil of their deeds is made fairseeming unto them. Allah guideth not the disbelieving folk.