Makhramah bin Bukayr (may Allah have mercy on him) narrates from his father that he asked Sa'id bin al-Musayyib (may Allah have mercy on him): Is it permissible for the Muslims to fight the disbelievers in the sacred months? He said: Yes! And Sulayman bin Yasar (may Allah have mercy on him) also said the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17747