Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 513
Narrated 'Abdul 'Aziz bin Suhaib:
Anas bin Malik said, "The Prophet took Safiya as a captive. He manumitted her and married her." Thabit asked Anas, "What did he give her as Mahr (i.e. marriage gift)?" Anas replied. "Her Mahr was herself, for he manumitted her."