Musnad Ahmad 790:186

'Affan narrated to us, Hammad bin Salamah narrated to us, from 'Ata' al-Khurasani, from Sa'id bin al-Musayyib, from the Prophet, peace and blessings of Allah be upon him. And Ayyub, Hisham, and Habib, from Muhammad bin Sirin, from 'Imran bin Husayn, from the Prophet, peace and blessings of Allah be upon him. And Humayd, Yunus, Qatadah, and Simak bin Harb, from al-Hasan, from 'Imran bin Husayn, from the Prophet, peace and blessings of Allah be upon him: "A man emancipated six slaves of his at the time of his death, and he had no wealth other than them. So the Messenger of Allah, peace and blessings of Allah be upon him, drew lots between them, returned four to slavery, and emancipated two."