Musnad Ahmad 1014:11

Ishaq ibn Isa narrated to us, Hushaym narrated to us, from Khalid al-Hadhdha, from Abu Qilabah, from Abu Zayd al-Ansari, that a man emancipated six slaves at the time of his death, and he had no wealth other than them. The Messenger of Allah (peace and blessings of Allah be upon him) drew lots among them, so he emancipated two and kept four in servitude.