Sahih Bukhari
Fighting for the Cause of Allah (Jihaad)
Volume: 004 / Book Number: 052 / Hadith Number: 239
Narrated Ibrahim Abu Isma'il As-Saksaki:
I heard Abu Burda who accompanied Yazid bin Abi Kabsha on a journey. Yazid used to observe fasting on journeys. Abu Burda said to him, "I heard Abu Musa several times saying that Allah's Apostle said, 'When a slave falls ill or travels, then he will get reward similar to that he gets for good deeds practiced at home when in good health."