Al-Baqarah 2:217

يَسۡـَٔلُونَكَ عَنِ ٱلشَّهۡرِ ٱلۡحَرَامِ قِتَالٖ فِيهِۖ قُلۡ قِتَالٞ فِيهِ كَبِيرٞۚ وَصَدٌّ عَن سَبِيلِ ٱللَّهِ وَكُفۡرُۢ بِهِۦ وَٱلۡمَسۡجِدِ ٱلۡحَرَامِ وَإِخۡرَاجُ أَهۡلِهِۦ مِنۡهُ أَكۡبَرُ عِندَ ٱللَّهِۚ وَٱلۡفِتۡنَةُ أَكۡبَرُ مِنَ ٱلۡقَتۡلِۗ وَلَا يَزَالُونَ يُقَٰتِلُونَكُمۡ حَتَّىٰ يَرُدُّوكُمۡ عَن دِينِكُمۡ إِنِ ٱسۡتَطَٰعُواْۚ وَمَن يَرۡتَدِدۡ مِنكُمۡ عَن دِينِهِۦ فَيَمُتۡ وَهُوَ كَافِرٞ فَأُوْلَـٰٓئِكَ حَبِطَتۡ أَعۡمَٰلُهُمۡ فِي ٱلدُّنۡيَا وَٱلۡأٓخِرَةِۖ وَأُوْلَـٰٓئِكَ أَصۡحَٰبُ ٱلنَّارِۖ هُمۡ فِيهَا خَٰلِدُونَ 217

They ask you about the sacred month - about fighting therein. Say, "Fighting therein is great [sin], but averting [people] from the way of Allah and disbelief in Him and [preventing access to] al-Masjid al-Haram and the expulsion of its people therefrom are greater [evil] in the sight of Allah. And fitnah is greater than killing." And they will continue to fight you until they turn you back from your religion if they are able. And whoever of you reverts from his religion [to disbelief] and dies while he is a disbeliever - for those, their deeds have become worthless in this world and the Hereafter, and those are the companions of the Fire, they will abide therein eternally