Musnad Ahmad 30:350

Yazid narrated to us, Sa'id narrated to us, from Qatadah, from an-Nadr ibn Anas, from Bashir ibn Nahik, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever has a share in a slave and emancipates his half, then he is responsible for his full liberation if he has wealth. If he does not have wealth, the slave is to work to earn the price of his own neck, without being overburdened."