al-Laith bin Sa'd الليث بن سعد · The Book of Manumission of Slaves

The Messenger of Allah (ﷺ) said to us: If one of you has a slave, and he enters into an agreement to purchase his freedom, and can pay the full price, she must veil herself from him.

A man emancipated six slaved at the time of his death and he had no other property. The Prophet (ﷺ) was informed about it. He cast lots among them, emancipated two and retained four in slavery.