Sahih Bukhari Volume 004, Book 052, Hadith Number 042.

Narated By Ibn 'Abbas : Allah's Apostle said, "There is no Hijra (i.e. migration) (from Mecca to Medina) after the Conquest (of Mecca), but Jihad and good intention remain; and if you are called (by the Muslim ruler) for fighting, go forth immediately.