And because it may be too great a temptation to human frailty, apt to grasp at power, for the same persons, who have the power of making laws, to have also in their hands the power to execute them, whereby they may exempt themselves from obedience to the laws they make, and suit the law, both in its making, and execution, to their own private advantage...
Second Treatise of Civil Government, Ch. XII, sec. 143 - Two Treatises of Government (1689)