Hadith.4849 - Muhammad ibn Humran asked Abu Abdullah عليه السلام about whether a slave is obligated to perform ẓihar (a form of divorce by comparison).
Imam عليه السلام replied: "He is required to fulfill half of what is required of a free man, which is fasting for one month. However, he is not obligated to offer expiation through charity or the freeing of a slave."