Musnad Abu Ya'la al-Mawsili 109:229

Abu Khaythama narrated to us, Rawh ibn ‘Ubadah narrated to us, Ibn Jurayj narrated to us, he said: Abu al-Zubayr informed me that he heard Jabir ibn ‘Abd Allah saying: The Prophet, may Allah bless him and grant him peace, wrote regarding every clan [that they are responsible for] their blood money. Then he wrote that it is not lawful for a client [mawla] of a Muslim man to be taken [as a client] without his permission.