Musannaf Ibn Abi Shaybah 29520 — The ruler who errs in a prescribed

Shu'bah said: I asked al-Hakam and Hammad about two men who testified against a man, so his hand was cut off, and then people looked into it and one of the two witnesses turned out to be a slave. What is the ruling in this case? Both of them said: The ruler (imam) will be held liable.