Musannaf Ibn Abi Shayba 28:779

Abu Khalid al-Ahmar narrated to us, from Ash'ath, from Muhammad, who said regarding the spoils of war: "One-fifth is for Allah, and a share is for the Prophet, may Allah bless him and grant him peace, and the *Safiyy* (the chosen portion)." Ibn Sirin said: "The best head [of captives] from the prisoners is taken for the Prophet, may Allah bless him and grant him peace. Then the fifth is extracted, and then a share is allotted to him along with the people, whether he was absent or present." Ibn Sirin said: "The *Safiyy* on the day of Khaybar was Safiyyah bint Huyayy." Al-Sha'bi said: "The *Safiyy* on the day of Khaybar was Safiyyah bint Huyayy; the Messenger of Allah, may Allah bless him and grant him peace, took her in marriage."