You do not belong to any bona fide religion that prohibits killing?
I presume I could classify myself as a Christian, said Sutton. I believe there is a Commandment about killing.
The robot shook his head. It doesn't count.
It is clear and specific, Sutton argued. It says, 'Thou shalt not kill.'
It is all of that, the robot told him. But it has been discredited. You humans discredited it yourselves. You never obeyed it. You either obey a law or you forfeit it. You can't forget it with one breath and invoke it with the next.

Chapter V (pp. 27-28) - Time and Again (1951)