Sayyidah Aishah (may Allah be pleased with her) said: When the people of Makkah sent the ransoms for their captives, Zaynab, the daughter of the Messenger of Allah (peace and blessings be upon him), sent as ransom for Abu al-As the necklace which Sayyidah Khadijah (may Allah be pleased with her) had given Zaynab at the time of her marriage to Abu al-As. When the Messenger of Allah (peace and blessings be upon him) saw it, he was overcome with tenderness, and he (peace and blessings be upon him) said: "If you see fit, release Zaynab's captive and return her ransom to her." They said: Yes, O Messenger of Allah. So they released him and returned her ransom. Sayyiduna al-Abbas (may Allah be pleased with him) said: O Messenger of Allah, I am a Muslim. The Messenger of Allah (peace and blessings be upon him) said: "Allah knows best about your Islam. If it is truly as you say, Allah will reward you for it. So pay the ransom for yourself and your two nephews, Nawfal bin al-Harith and Aqil bin Abi Talib, and for your ally Utbah bin Amr bin Jahdam of Banu al-Harith bin Fihr." Al-Abbas (may Allah be pleased with him) said: O Messenger of Allah, I have nothing. He (peace and blessings be upon him) said: "Then where is the wealth that you and Umm al-Fadl (may Allah be pleased with her) buried, when you said to her: 'If I am killed, this wealth is for my sons al-Fadl, Abdullah and Qutham'?" Al-Abbas (may Allah be pleased with him) said: By Allah, O Messenger of Allah, I know that you are the Messenger of Allah; this was something no one knew except me and Umm al-Fadl (may Allah be pleased with her). So, O Messenger of Allah, count towards my ransom the twenty uqiyah of wealth I had with me, which you took. The Messenger of Allah (peace and blessings be upon him) said: "I will do so." So al-Abbas (may Allah be pleased with him) paid the ransom for himself, his two nephews and his ally, and Allah Almighty revealed this verse: "O Prophet, say to the captives who are in your hands: If Allah knows any good in your hearts, He will give you better than what was taken from you, and He will forgive you; and Allah is Forgiving, Merciful" [Surah al-Anfal: 70]. So in Islam Allah gave me twenty slaves in place of the twenty uqiyah, each of them with wealth in his hand to trade with, besides what I hope for of the forgiveness of Allah, the Mighty and Majestic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12849