Musnad Ahmad 283:8

Muhammad ibn Idris al-Shafi‘i narrated to us, he said: Malik narrated to us, from Abu Layla ‘Abd Allah ibn ‘Abd al-Rahman ibn Sahl ibn Abi Hathma, that Sahl ibn Abi Hathma informed him, and men from the elders of his people: That the Messenger of Allah (peace and blessings of Allah be upon him) said to Huwayyisa, Muhayyisa, and ‘Abd al-Rahman: "Will you take an oath and claim the blood of your companion?" They said: "No." He said: "Then will the Jews take an oath?" They said: "They are not Muslims." So the Prophet (peace and blessings of Allah be upon him) paid the blood money for him from his own [resources].