Hadith.4868 - Al-ʿAlaʾ narrated from Muḥammad ibn Muslim from one of the two Imams (peace be upon them), who said
"The divorce of a bondwoman is through her sale or the sale of her husband."
Imam (as) also said regarding a man who marries his bondwoman to a free man and then sells her: "This constitutes separation between them unless the buyer wishes to let them remain together."