It was narrated from 'Aishah:
that the Messenger of Allah (ﷺ) set Safiyyah free, and made her ransom her dowry, and he married her. (JA)
English reference (JA): Vol. 3, Book 9, Hadith 1958 (JA)
Arabic reference (JA): Book 9, Hadith 2034 (JA)