‘Abd al-Rahman ibn ‘Awf was sent on a Mission to win over the Banu Kalb tribe and get them to adopt Islam and side with the Muslims, this operation was carried out successfully.
Muhammad appointed ‘Abd al-Rahman ibn ‘Awf to head to Dumatul Jandal to win over the people.
[2][7]‘Abd al-Rahman set out with 700 men on an expedition to Dumat al-Jandal, that is on the route to Khaybar, Fadak.
[2] Muhammad received the news through a Messenger, and then instructed ‘Abd al-Rahman to marry Tamadhir, the daughter of the Christian chief, Al-Asbagh.
So ‘Abd al-Rahman married Tumadhir bint Asbagh, the daughter of the Christian king and brought this lady with him to Medina.