intercalating a month is adding to unbelief. the unbelievers are misguided by this for they take the same month to be sacred one year and sacrilegious the next thus making the number of months sanctified by god accord with theirs in order to make what god has forbidden lawful. attractive seem to them their evil deeds but god does not show the unbelievers the way.
إنما النسيء زيادة في الكفر يضل به الذين كفروا يحلونه عاما ويحرمونه عاما ليواطئوا عدة ما حرم الله فيحلوا ما حرم الله زين لهم سوء أعمالهم والله لا يهدي القوم الكافرين