Sec. 159. WHERE the legislative and executive power are in distinct hands, (as they are in all moderated monarchies, and well-framed governments) there the good of the society requires, that several things should be left to the discretion of him that has the executive power: for the legislators not being able to foresee, and provide by laws, for all that may be useful to the community, the executor of the laws having the power in his hands, has by the common law of nature a right to make use of it for the good of the society, in many cases, where the municipal law has given no direction, till the legislative can conveniently be assembled to provide for it. Many things there are, which the law can by no means provide for; and those must necessarily be left to the discretion of him that has the executive power in his hands, to be ordered by him as the public good and advantage shall require: nay, it is fit that the laws themselves should in some cases give way to the executive power, or rather to this fundamental law of nature and government, viz. That as much as may be, all the members of the society are to be preserved: for since many accidents may happen, wherein a strict and rigid observation of the laws may do harm; (as not to pull down an innocent man's house to stop the fire, when the next to it is burning) and a man may come sometimes within the reach of the law, which makes no distinction of persons, by an action that may deserve reward and pardon; 'tis fit the ruler should have a power, in many cases, to mitigate the severity of the law, and pardon some offenders: for the end of government being the preservation of all, as much as may be, even the guilty are to be spared, where it can prove no prejudice to the innocent.
John Locke, Second Treatise
http://www.constitution.org/jl/2ndtr14.htm
U.S. Constitution, Article II Section I. The executive Power shall be vested in a President of the United States of America.
John Locke, Second TreatiseOf Prerogative.
Sec. 159. WHERE the legislative and executive power are in distinct hands, (as they are in all moderated monarchies, and well-framed governments) there the good of the society requires, that several things should be left to the discretion of him that has the executive power: for the legislators not being able to foresee, and provide by laws, for all that may be useful to the community, the executor of the laws having the power in his hands, has by the common law of nature a right to make use of it for the good of the society, in many cases, where the municipal law has given no direction, till the legislative can conveniently be assembled to provide for it. Many things there are, which the law can by no means provide for; and those must necessarily be left to the discretion of him that has the executive power in his hands, to be ordered by him as the public good and advantage shall require: nay, it is fit that the laws themselves should in some cases give way to the executive power, or rather to this fundamental law of nature and government, viz. That as much as may be, all the members of the society are to be preserved: for since many accidents may happen, wherein a strict and rigid observation of the laws may do harm; (as not to pull down an innocent man's house to stop the fire, when the next to it is burning) and a man may come sometimes within the reach of the law, which makes no distinction of persons, by an action that may deserve reward and pardon; 'tis fit the ruler should have a power, in many cases, to mitigate the severity of the law, and pardon some offenders: for the end of government being the preservation of all, as much as may be, even the guilty are to be spared, where it can prove no prejudice to the innocent.
U.S. Constitution, Article II Section I. The executive Power shall be vested in a President of the United States of America.