Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4712
It has been narrated on the authority of Uqba b. Amir who said: I heard the Messenger of Allah (may peace be upon him) say: Lands shall be thrown open to you and Allah will suffice you (against your enemies), but none of you should give up playing with his arrows.