Sahih Bukhari Volume 004, Book 052, Hadith Number 079.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 52. Fighting for the Cause of Allah (Jihaad)
Narated By Ibn 'Abbas : On the day of the Conquest (of Mecca) the Prophet said, "There is no emigration after the Conquest but Jihad and intentions. When you are called (by the Muslim ruler) for fighting, go forth immediately." (See Hadith No. 42)