Fighting for the Cause of Allah (Jihaad)
Bukhari :: Book 4 :: Volume 52 :: Hadith 81
Narrated Anas bin Malik
In the life-time of the Prophet, Abu Talha did not fast because of the Jihad, but after the Prophet died I never saw him without fasting except on 'Id-ul-Fitr and 'Id-ul-Aclha.