Musannaf Ibn Abi Shayba 13:1773

Abu Bakr narrated to us, he said: Abu Mu’awiyah narrated to us, from Hajjaj, from ‘Amr ibn Shu’ayb, from Sa’id ibn al-Musayyib, who said: Thirty of the companions of the Messenger of Allah (may Allah bless him and grant him peace) used to guarantee for the man who emancipated a slave [owned] between him and his partner, if he was wealthy.