Ат-Тавба 9:6

When the Muslims attained a strong position, the Quraysh entered into treaties with them. However, the Quraysh were not happy with these agreements. They thought that their execution of these treaties with their ‘enemy’ was very much to their detriment. That is why they were always on the look-out for opportunities to violate their agreements and cause harm to Muslims or at least defame them. Obviously, when there is a clear breach of a treaty by one party, the carrying out of the agreement by the other party is no longer obligatory. This was the thinking of the Quraysh who felt that, with the rise of the Muslims, their leadership was at stake. However, there were other tribes (Banu Kinana, Banu Khuza’a, Banu Dhamra) who, unhampered by this psychological complication, had executed agreements with the Muslims and fulfilled them. When a period of respite of four months was announced, about nine months remained until the expiry of the periods of these agreements. The order was that these agreements be honoured till the last date, because that was the requirement of God-fearing. But after the expiry of this period, no such agreement was entered into with anybody and there were only two alternatives before the polytheists—either to embrace Islam or be ready for war.