“In taking revenge, a man is but even with his enemy; but in passing it over, he is superior.”

De Hierosolymitana peregrinatione acceleranda (1189), cited from Mary Beth Rose (ed.) Women in the Middle Ages and Renaissance (Syracuse, NY: Syracuse University Press, 1986) p. 29; translation from John Simpson The Concise Oxford Dictionary of Proverbs (Oxford: Oxford University Press, 1993) p. 55.
A similar proverb, Qui son nez cope deshonore son vis, appears in the late 12th century chanson de geste Garin le Loheren, line 2877.

Mustadrak al-Wasa’il, Volume 4, Page 237
Shi'ite Hadith

Ibid., p. 267
The Book of Disquiet
Original: Por enquanto, visto que vivemos em sociedade, o único dver dos superiores é reduzirem ao mínimo a sua participação na vida da tribo. Não ler jornais, ou lê-los só para saber o que de pouco importante ou curioso se passa.
[...] O supremo estado honroso para um homem superior é não saber quem é o chefe de Estado do seu país, ou se vive sob monarquia ou sob república.
Toda a sua atitude deve ser colocar-se a alma de modo que a passagem das coisas, dos acontecimentos não o incomode. Se o não fizer terá que se interessar pelos outros, para cuidar de si próprio.

1940s–present, Introduction to Nietzsche's The Antichrist

Source: I Know Why the Caged Bird Sings

The Analects, The Doctrine of the Mean
Context: To show forbearance and gentleness in teaching others; and not to revenge unreasonable conduct — this is the energy of southern regions, and the good man makes it his study. To lie under arms; and meet death without regret — this is the energy of northern regions, and the forceful make it their study. Therefore, the superior man cultivates a friendly harmony, without being weak — How firm is he in his energy! He stands erect in the middle, without inclining to either side — How firm is he in his energy! When good principles prevail in the government of his country, he does not change from what he was in retirement. How firm is he in his energy! When bad principles prevail in the country, he maintains his course to death without changing — How firm is he in his energy!

Proverbs 19:11, New World Translation of the Holy Scriptures

Source: The Doctrine of the Mean