“For instance, if you have by a lie hindered a man who is even now planning a murder, you are legally responsible for all the consequences. But if you have strictly adhered to the truth, public justice can find no fault with you, be the unforeseen consequence what it may. It is possible that whilst you have honestly answered Yes to the murderer’s question, whether his intended victim is in the house, the latter may have gone out unobserved, and so not have come in the way of the murderer, and the deed therefore have not been done; whereas, if you lied and said he was not in the house, and he had really gone out (though unknown to you) so that the murderer met him as he went, and executed his purpose on him, then you might with justice be accused as the cause of his death. For, if you had spoken the truth as well as you knew it, perhaps the murderer while seeking for his enemy in the house might have been caught by neighbours coming up and the deed been prevented.”

'Where Do We Go From Here?" as published in Where Do We Go from Here : Chaos or Community? (1967), p. 62; many statements in this book, or slight variants of them, were also part of his address Where Do We Go From Here?" which has a section below. A common variant appearing at least as early as 1968 has "Returning violence for violence multiplies violence..." An early version of the speech as published in A Martin Luther King Treasury (1964), p. 173, has : "Returning hate for hate multiplies hate..."
1960s
Context: The ultimate weakness of violence is that it is a descending spiral, begetting the very thing it seeks to destroy. Instead of diminishing evil, it multiplies it. Through violence you may murder the liar, but you cannot murder the lie, nor establish the truth. Through violence you may murder the hater, but you do not murder hate. In fact, violence merely increases hate. So it goes. … Returning hate for hate multiplies hate, adding deeper darkness to a night already devoid of stars. Darkness cannot drive out darkness: only light can do that. Hate cannot drive out hate: only love can do that.

"Three Poems of the Atomic Bomb: Dirge for the New Sunrise"
The Canticle of the Rose (1949)

Preface to The Practice of Prelates (1531).
Context: Take heed, therefore, wicked prelates, blind leaders of the blind; indurate and obstinate hypocrites, take heed …. Ye will be the chiefest in Christ's flock, and yet will not keep one jot of the right way of his doctrine …ye keep thereof almost naught at all, but whatsoever soundeth to make of your bellies, to maintain your honour, whether in the Scripture, or in your own traditions, or in the pope's law, that ye compel the lay-people to observe; violently threatening them with your excommunications and curses, that they shall be damned, body and soul, if they keep them not. And if that help you not, then ye murder them mercilessly with the sword of the temporal powers, whom ye have made so blind that they be ready to slay whom ye command, and will not hear his cause examined, nor give him room to answer for himself.

Source: A Study in Scarlet

Crime and Punishment (1866)

If we do not, then we should look somewhere else.
Source: Books, Spiritual Warrior, Volume III: Solace for the Heart in Difficult Times (Hari-Nama Press, 2000), Chapter 8 - How To Strengthen Ourselves

"The Fool-Killer"
The Voice of the City (1908)
Context: I know you. I have heard of you all my life. I know now what a scourge you have been to your country. Instead of killing fools you have been murdering the youth and genius that are necessary to make a people live and grow great. You are a fool yourself, Holmes; you began killing off the brightest and best of our countrymen three generations ago, when the old and obsolete standards of society and honor and orthodoxy were narrow and bigoted. You proved that when you put your murderous mark upon my friend Kerner — the wisest chap I ever knew in my life.

Source: Mortal Coil

1960s, Where Do We Go from Here: Chaos or Community? (1967)