Surah Al Anfal Tafseer

فَكُلُواْ مِمَّا غَنِمْتُمْ حَلَلاً طَيِّبًا

So enjoy what you have gotten of booty in war, lawful and good.

The Muslims then took the ransom for their captives.

وَاتَّقُواْ اللّهَ إِنَّ اللّهَ غَفُورٌ رَّحِيمٌ

and have Taqwa of Allah. Certainly, Allah is Oft-Forgiving, Most Merciful.

In his Sunan, Imam Abu Dawud recorded that Ibn Abbas said that;

the Messenger of Allah fixed four hundred (Dirhams) in ransom from the people of Jahiliyyah in the aftermath of Badr.

The majority of the scholars say that;

the matter of prisoners of war is up to the Imam. If he decides, he can have them killed, such as in the case of Bani Qurayzah. If he decides, he can accept a ransom for them, as in the case of the prisoners of Badr, or exchange them for Muslim prisoners. The Messenger exchanged a woman and her daughter who were captured by Salamah bin Al-Akwa, for exchange of some Muslims who were captured by the idolators, or if he decides he can take the prisoner as a captives