All laws stand on the best and broadest basis which go to enforce moral and social duties: Though indeed it is not every moral and social duty the neglect of which is the ground of an action. For there are, which are called in the civil law, duties of imperfect obligation, for the enforcing of which no action lies.

Per Lord Kenyon C.J. in Pasley v Freeman (1789) E.3 T.R.51

… in the absence of an expressed constitutional or legal provision, it could not follow from the mere fact that a rule violated standards of morality that it was not a rule of law; and, conversely, it could not follow from the mere fact that a rule was morally desirable that it was a rule of law.

Positivism and the Separation of Law and Morals, H.L.A. Hart, , 71 Harv. L. Rev. 593, 598

If we felt that the law itself was our safest refuge, would it not be because even in the most perverted regimes there is a certain hesitancy about writing cruelties, intolerance, and inhumanities into law? And is it not clear that this hesitancy itself derives, not from a separation of law and morals, but precisely from an identification of law with those demands of morality that are the most urgent and the most obviously justifiable, which no man need be ashamed to profess?

Positivism and Fidelity to Law, Lon Fuller, A Reply to Professor Hart,71 Harv. L. Rev. 630, 637