Sahih Muslim Book 19, Hadith Number 4327.

Chapter : The spoils of war specially made lawful for this Umma.

It has been narrated by Abu Huraira that the Messenger of Allah (may peace be upon him) said: One of the Prophets made a holy war. He said to his followers: One who has married a woman and wants to consummate to his marriage but has not yet done so; another who has built a house but has not yet erected its roof; and another who has bought goats and pregnant she-camels and is waiting for their offspring-will not accompany me. So he marched on and approached a village at or about the time of the ‘Asr prayers. He said to the sun: Thou art subservient (to Allah) and so am I. O Allah, stop it for me a little. It was stopped for him until Allah granted him victory. The people gathered the spoils of war (at one place). A fire approached the spoils to devour them, but it did not devour them. He (the Holy Prophet) said: Some of you have been guilty of misappropriation. So one man from each tribe should swear fealty to me. The did so (putting their hands into his). The hand of one man stuck to his hand and the Prophet (may peace be upon him) said: Your tribe is guilty of misappropriation. Let all the members of your tribe swear fealty to me one by one. They did so, when the hands of two or three persons got stuck with his hand. He said: You have misappropriated. So they took out gold equal in volume to the head of a cow. They-placed it among the spoils on the earth. Then the fire approached the spoils and devoured them. The spoils of war were not made lawful for any people before us, This is because Allah saw our weakness and humility and made them lawful for us.