From Sahih Muslim (Hadith 4822):
It has been narrated on the authority of Yazid b. Abu Ubaid (the freed slave of Salama b. al-Akwa') who said:1 asked Salama as to what effect he had sworn fealty to the Messenger of Allah (ﷺ) on the Day of Hudaibiya. He said: To the effect that we will die fighting
Reference: Muslim 4822