The Expedition of ʿAbdullah ibn Jahsh and the verse on the sacred months
The Prophet ﷺ sent ʿAbdullah ibn Jahsh with a small party to Nakhla to watch a Quraysh caravan. They killed a man on the last day of the sacred month of Rajab; Quraysh raised an outcry, and Allah sent down His decisive ruling on fighting in the sacred month.
The Prophet ﷺ gave ʿAbdullah ibn Jahsh a letter and ordered him not to open it until after two days. When he opened it, it directed him to Nakhla, between Makkah and al-Taʾif, to watch Quraysh. He said: To hear is to obey, and his companions went with him willingly.
A Quraysh caravan bearing trade passed by them, and the party — for it was the last day of Rajab — deliberated between violating the sacred month or letting the caravan escape. They loosed arrows, killed ʿAmr ibn al-Hadrami and captured two men. The Prophet ﷺ deferred the matter and censured them.
Quraysh spread the claim that Muhammad had made lawful the sacred month, so Allah revealed: "They ask you about the sacred month — about fighting in it. Say: fighting in it is a great sin, but averting from the path of Allah and disbelief in Him... and persecution is worse than killing." The verse set the balance: the month's sanctity is great, but turning people from their religion is greater.
Note — differing reports on the date: The fighting was on the last day of Rajab 2 AH according to the well-known view; some say the first night of Shaʿban, owing to uncertainty in sighting the crescent.