Musannaf Ibn Abi Shayba 13:925

Abu Bakr narrated to us, he said: Shareek narrated to us, from Jabir, from Amir, that Umar ibn al-Khattab said: If she was a previously married woman (thayyib), he returns half of the tenth (one-twentieth of the dowry). And if she was a virgin (bikr), he returns the tenth (one-tenth of the dowry).