Surah At-Tawbah 9:37

إِنَّمَا ٱلنَّسِىٓءُ زِيَادَةٌ فِى ٱلْكُفْرِ ۖ يُضَلُّ بِهِ ٱلَّذِينَ كَفَرُوا۟ يُحِلُّونَهُۥ عَامًا وَيُحَرِّمُونَهُۥ عَامًا لِّيُوَاطِـُٔوا۟ عِدَّةَ مَا حَرَّمَ ٱللَّهُ فَيُحِلُّوا۟ مَا حَرَّمَ ٱللَّهُ ۚ زُيِّنَ لَهُمْ سُوٓءُ أَعْمَـٰلِهِمْ ۗ وَٱللَّهُ لَا يَهْدِى ٱلْقَوْمَ ٱلْكَـٰفِرِينَ

Indeed, the postponing [of restriction within sacred months] is an increase in disbelief by which those who have disbelieved are led [further] astray. They make it lawful one year and unlawful another year to correspond to the number made unlawful by Allāh and [thus] make lawful what Allāh has made unlawful. Made pleasing to them is the evil of their deeds; and Allāh does not guide the disbelieving people.

Translation: Saheeh International

Tafsir

Postponement of the sacred month — that is the deferment of the sacredness of a given month to another as they used to do during paganism such as postponing the sacredness of Muharram if it arrives while they are at war to Safar — is only an excess of unbelief because of their rejection of God’s ruling thereof whereby …

Excerpt from Tafsir al-Jalalayn, commentary on 9:37, via Quran.com. The reader has the full commentary and 9 more tafsirs.