Sayyiduna Imran bin Husayn (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) ransomed one man in exchange for two men.
(b) The woman whom Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) gave to the Messenger of Allah (peace and blessings be upon him), the Messenger of Allah (peace and blessings be upon him) obtained several captives in exchange for her.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18826
Sayyiduna Abu Musa (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Feed the hungry, free the captive, and visit the sick." Sufyan says that al-'ani means captives.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18827
Abu Juhayfah says: I said to Sayyiduna Ali (may Allah be pleased with him): "O Commander of the Believers! Do you have anything special from revelation?" He said: "Nothing at all. By the One who split the seed and created the soul, (there is nothing) except the understanding that Allah grants to a person, and what is in this scroll." I asked: What is in the scroll? He said: "(Rulings) about blood-money and the freeing of captives, and that 'a believer shall not be killed in retaliation for a polytheist.'" Then he says: I asked Mutarrif: What is freeing the captive? He said: That he be freed from the enemy; the Sunnah has run in this way. And Mutarrif says that al-'aql means paying blood-money.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18828