Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 487
Narrated Yazid bin Abi Ubaid:
I said to Salama bin Al-Akwa, "For what did you give the Pledge of allegiance to Allah's Apostle on the day of Al-Hudaibiya?" He replied, "For death (in the Cause of Islam.)."