Full Idea
One drives nature out of morality when one say "love your enemies": for then the natural "Thou shalt love thy neighbour and hate thy enemy" in the law (in instinct) has become meaningless.
Gist of Idea
'Love your enemy' is unnatural, for the natural law says 'love your neighbour and hate your enemy'
Source
Friedrich Nietzsche (The Will to Power (notebooks) [1888], §204)
Book Reference
Nietzsche,Friedrich: 'The Will to Power', ed/tr. Kaufmann,W /Hollingdate,R [Vintage 1968], p.120
A Reaction
When the stoics said 'live according to nature' they meant according to reason, which presumably compromises with enemies. Profoundly Christian acts may be unnatural, but they are very moving.