Musannaf Ibn Abi Shaybah

Hazrat Abu Alaa narrates that Hazrat Qatadah and Hazrat Abu Hashim were asked about a man who intentionally killed someone, so he was imprisoned in order for retribution (qisas) to be taken from him. Then another man came and intentionally killed him. Both of them said: Retribution (qisas) will not be taken from him.

Hazrat Muammar states that Hazrat Zuhri said: When a person has committed murder intentionally, and then another person intentionally kills that murderer, then since the one in the middle was to be killed anyway, there is no retribution (qisas) for him.