Yas-aloonaka AAani al-anfali quli al-anfalu lillahi warrasooli fattaqoo Allaha waaslihoo thata baynikum (surah Anfal: 1)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(8:1) They ask you concerning the spoils of war? Tell them: 'The spoils of war belong to Allah and the Messenger. So fear Allah, and set things right between you, and obey Allah and His Messenger if you are true believers.  *1

Yas`aloonaka `anil anfaali qulil anfaalu lillaahi war Rasooli fattaqul laaha wa ahlihoo zaata bainikum wa atee`ul laaha wa Rasoolahooo in kuntum mu`mineen

*1). The critique of the battle opens with this unusual note. Some disagreements had arisen among the Muslims with regard to sharing the spoils of war. As it was their first experience of fighting under the banner of Islam, the Muslim soldiers had scarcely any notion of the regulations they were required to follow on the battlefield and for settling problems arising from warfare. Doubtlessly some preliminary instructions had been laid down for them in Surah al-Baqarah 2 and Surah Muhammad 47, (See 2: 190 ff. and 47: 4 ff. - Ed.) However the full set of regulations that could contribute to civilizing the conduct of warfare had yet to be laid down. Hence, when it came to war as with several other societal matters, the Muslims were still under the influence of pre-Islamic ideas and concepts. Going by the age-old Arab customs, those who had seized the spoils of war considered themselves their sole and legitimate owners. On the other hand, the Muslims who had concentrated on driving away the enemy rather than on collecting the spoils, claimed that they deserved an equal share of the spoils. They contended that had they slackened in their duty of pursuing the enemy, the latter might have struck back, turning the Muslim victory into a defeat. Similarly, another group of Muslims who had escorted the Prophet (peace he on him) on the battlefield, also laid claim to an equal share, For, they believed, it was they who had rendered an invaluable service insofar as neglect of duty on their part might have resulted in endangering the precious life of the Prophet (peace be on him), in which case the possibility of victory and its attendant spoils and their distribution would all have been totally out of the question. Nonetheless, the group of Muslims who already possessed the spoils saw no merit in these claims. Arguments and counter-arguments gave rise to bitterness and bad blood. (For disagreements among Muslims on the question of distribution of spoils of war see Ibn Hisham, vol. 1. pp. 641-2; al-Waqadi, vol. 1, p. 78. See also the comments on the verse in Qurtubi and Ibn Kathir - Ed.)
It was at this juncture that God revealed the present surah. The opening verse takes up this issue. 'They ask you concerning anfal' is the query with which the surah opens. The very use of the word anfal instead of ghana'im in the query implies the answer. For the word anfal, which is the plural of nafl, stands for that which is extra, that which is over and above what is obligatory. If this extra is from the servant, it denotes that additional service which he voluntarily renders over and above what is obligatory. On the other hand, when this extra is from the master, it denotes the additional reward which the master awards his servant over and above what he is entitled to. What is being conveyed here by using the word anfal is, in fact, that all wrangling about spoils is out of place since it concerns not their rights, but the additional rewards they might receive from God. Any and all heated discussion in which they engaged was irrelevant since it was entirely for God to decide whether He should grant any extra reward or not; and if He should grant it, then how much, and to whom. In short, it was not for men to say who should and who should not receive any party of the spoils.
This was a major conceptual reform. The war that a Muslim wages is not in order to accumulate worldly benefits. He resorts to it for the moral and social reform of the world and does so when the opposing forces make it impossible to bring about reform by means of persuasion and preaching. Being reformers, the Muslims should focus their attentions on their goal - the reform of the world - rather than on the material benefits which accrue to them incidental by way of God's additional reward in lieu of their strivings. If the attention of Muslims is not diverted from material benefits to their true mission, it is likely that material benefits would become an end in themselves.
Moreover, the concept introduced by the Qur'an (see the verse above) also brought about a major administrative reform pertaining to war and the spoils of war. Before the advent of Islam, a soldier used to appropriate all that he could lay his hands on, claiming to be its rightful owner, or else spoils were seized either by; the king or the commander of the army. In the former case, mutual conflicts ensued among soldiers of the victorious army, with the frequent result that their victory turned into defeat. On the other hand, if the spoils were seized by the commander of the army or the ruler, soldiers often concealed and stole the spoils. By declaring that the spoils belong to God and His Messenger, the Qur'an made it obligatory on all soldiers to commit all the spoils of war to the custody of the commander, concealing not even something as trivial as a sewing needle. Subsequently the Qur'an laid down an elaborate set of laws to distribute the spoils of war. According to it, one-fifth of the spoils is to be deposited in the public treasury for public welfare and to provide support for the poor, while four-fifths is to be distributed among the soldiers. (al-Anfal 8: 41 - Ed.) It thus put an end to the evils inherent in the old system.
A subtle point implicit in the above verse should not he overlooked. In the opening verse of the Surah nothing has been said beyond affirming the principle that the spoils belong to God and His Messenger. The problem as to how the spoils should be distributed was not touched upon. The Qur'an does however subsequently treat the question of distribution (see verse 41 below). It is significant that in this second instance the word used is a verbal derivative of ghanimah (spoils, booty) (see verse 41 below) whereas in the opening verse the word used is anfal.