Hadith.5270 - Ibn Mahbub narrated from Abu Muhammad Al-Wabishi who said
I asked Abu Abdullah (as) about a group of people who claimed that a slave had committed an offense warranting his execution, and the slave confessed to it.
Imam (as) said: "The confession of a slave is not valid against his master."
Imam (as) further said: "But if they establish evidence for what they claimed against the slave, they may take the slave for it or his master may ransom him."