Abu Ishaq (may Allah have mercy on him) says: I asked Sufyan (may Allah have mercy on him) about this statement of Allah Almighty: "They ask you about fighting in the sacred month. Say: Fighting in it is a great (sin)" [Surah al-Baqarah: 217]. He said: This ruling has been abrogated, and now there is no harm in fighting them in the sacred months or at other times.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17748