Surah al-Mumtahanah (The Woman Examined) 60 : 13

The Surah deals with two incidents, the time of the occurrence of which is well known historically. The first relates to Hatib bin Abz Balta’a, who, a little before the conquest of Makkah, had sent a secret letter to the Quraysh chiefs informing them of the Prophet’s intention to attack them. The second relates to the Muslim women, who had started emigrating from Makkah to Madīnah, after the conclusion of the Truce of Hudaibiyah, and the problem arose whether they also were to be returned to the disbelievers, like the Muslim men, according to the conditions of the Truce. The mention of these two things absolutely determines that this Surah came down during the interval between the Truce of Hudaibiyah and the Conquest of Makkah. Besides, there is a third thing also that has been mentioned at the end of the Surah to the effect: What should the Prophet make the women to pledge when they come to take the oath of allegiance before him as believers? About this part also the guess is that this too was sent down some time before the conquest of Makkah, for after this conquest a large number of the Quraysh women, like their men, were going to enter Islam simultaneously and had to be administered the oath of allegiance collectively.