Musannaf Ibn Abi Shayba 28:734

Hafs ibn Ghiyath narrated to us, from Abu Salamah, from Abu Hafsah, from Ali ibn Zayd, from Yusuf ibn Mihran, from Ibn Abbas, who said: Umar said: "Every captive who was in the hands of the polytheists from among the Muslims, his ransom is from the treasury (Bayt al-Mal) of the Muslims."