Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4597
It has been narrated on the authority of Ibn 'Abbas that the Messenger of Allah (may peace be upon him) said on the day of the Conquest of Mecca: There is no Hijra now, but (only) Jihad (fighting for the cause of Islam) and sincerity of purpose (have great reward) ; when you are asked to set out (on an expedition undertaken for the cause of Islam) you should (readily) do so.