The Quraysh sent Suhayl ibn Amr to negotiate the Treaty of Hudaybiyya with Prophet Muhammad. Suhayl had a vested interest in the outcome since two of his sons had converted to Islam, one of whom he was keeping captive.
The Muslim masses were surprised by the treaty though, which they saw as an insult. Umar ibn Al-Khattab was particularly outraged, later saying that on that day he "doubted the Prophet's prophethood like [he] had never doubted it before"
While on the surface the treaty looked like a setback, it set the stage for the Muslims' eventual victory over Quraysh.