Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 353
Narrated Anas bin Malik:
Some men of the Ansar requested Allah's Apostle to allow them to see him, they said, "Allow us to forgive the ransom of our sister's son, 'Abbas." The Prophet said, "By Allah, you will not leave a single Dirham of it!"