“Now I gazed upon him, no longer in a passionate frenzy, but in a cold contempt. I visualized long days and nights of vengeance, of fiendish ingenuity and complete consumation. My enemy was at my mercy; he lived; all the plans of hate and torture I had concieved through the long years of wrong and insult I would wreak upon him. My plans were carefully laid; I knew exactly what tortures I would use, how long I could inflict them without causing death, until my enemy at last went forth, a man ruined of soul and body. I was at peace, and content.”

Source: Andre Cornelis (1886), Ch. 4
Context: I once spoke to my aunt of the vow I had taken, the solemn promise I had made to myself that I would discover the murderer of my father, and take vengeance upon him, and she laid her hand upon my mouth. She was a pious woman, and she repeated the words of the gospel: "Vengeance is mine, saith the Lord." Then she added: "We must leave the punishment of the crime to Him; His will is hidden from us. Remember the divine precept and promise, 'Forgive and you shall be forgiven.' Never say: 'An eye for an eye, a tooth for a tooth.' Ah, no; drive this enmity out of your heart, Cornelis; yes, even this." And there were tears in her eyes.
My poor aunt! She thought me made of sterner stuff than I really was. There was no need of her advice to prevent my being consumed by the desire for vengeance which had been the fixed star of my early youth, the blood-colored beacon aflame in my night. Ah! the resolutions of boyhood, the "oaths of Hannibal" taken to ourselves, the dream of devoting all our strength to one single and unchanging aim — life sweeps all that away, together with our generous illusions, ardent enthusiasm, and noble hopes.

19th August 1826) Metrical Fragments - No. 1 (under the pen name Iole
The London Literary Gazette, 1826

Letter to William Strahan (5 July 1775); reported in Bartlett's Familiar Quotations, 10th ed. (1919).
Epistles

Sentencing (1880)

Source: Confessions of a Mask (1949), p. 220.

Source: Why We Broke Up

Final lines of his Richard Dimbleby lecture Shaking Hands With Death on euthanasia and assisted suicide, quoted in "Terry Pratchett: my case for a euthanasia tribunal" in The Guardian (2 February 2010) http://www.guardian.co.uk/society/2010/feb/02/terry-pratchett-assisted-suicide-tribunal
General sources
Context: I dare say that quite a few people have contemplated death for reasons that much later seemed to them to be quite minor. If we are to live in a world where a socially acceptable "early death" can be allowed, it must be allowed as a result of careful consideration.
Let us consider me as a test case. As I have said, I would like to die peacefully with Thomas Tallis on my iPod before the disease takes me over and I hope that will not be for quite some time to come, because if I knew that I could die at any time I wanted, then suddenly every day would be as precious as a million pounds. If I knew that I could die, I would live. My life, my death, my choice.

a Latin crime. It is a crime that shows traces of a cool, resourceful, deliberate brain — I think an Anglo-Saxon brain.
Murder on the Orient Express (1934)

DLS Reviews Interview https://www.dlsreviews.com/guy-n-smith-interview-001-march-2015.php (March 20, 2015)