Musnad Ahmad 33:330

'Abd al-Razzaq narrated to us, Ibn Jurayj informed us, and Rawh narrated to us, Ibn Jurayj informed us, Abu al-Zubayr informed me that he heard Jabir ibn 'Abd Allah saying: The Prophet, peace and blessings of Allah be upon him, wrote: "Upon every clan is its blood money (diya)." Then he wrote: "It is not lawful for the client (mawla) of a Muslim man to be taken as a client by another without his permission." Rawh said: "To be taken as a client (yatawalla)."