Sahih Muslim 1860a

Qutaybah ibn Said narrated to us; Hatim, meaning Ibn Ismail, narrated to us, from Yazid ibn Abi Ubayd, the client of Salamah ibn al-Akwa, who said: I asked Salamah, “On what did you pledge allegiance to the Messenger of Allah, peace and blessings be upon him, on the day of al-Hudaybiyyah?” He said, “To fight to the death.”