Musannaf Ibn Abi Shayba 35:392

Abu Khalid al-Ahmar narrated to us, from Hajjaj, from ‘Amr ibn Shu‘ayb, from his father, from his grandfather, that Huwayyisah, Muhayyisah, ‘Abdullah, and ‘Abdur-Rahman, the sons of so-and-so, went out to procure provisions in Khaybar. Then, an assault was made upon ‘Abdullah, and he was killed. He said: They mentioned that to the Prophet, may Allah bless him and grant him peace. He said: The Messenger of Allah, may Allah bless him and grant him peace, said: "You shall swear fifty oaths and be entitled to the claim." They said: "O Messenger of Allah, how shall we swear when we did not witness it?" He said: "Then the Jews shall exonerate you [by swearing]." They said: "O Messenger of Allah, then the Jews will kill us." He said: So the Messenger of Allah, may Allah bless him and grant him peace, paid the blood money for him from his own [resources].