“said the Roman poet Terence: 'Nothing human is alien to me.' The slogan of the old Immigration and Naturalization Service could have been the reverse: To us, no aliens are human.”

Act I, scene 1, line 25 (77).
Variant translations:
I am a human and consider nothing human alien to me.
I am human, I consider nothing human to be alien to me.
I am human, therefore nothing relating to humanity is outside of my concern.
I am a man; I consider nothing human alien to me.
I am a man, I regard nothing that is human alien to me.
I am a man, I count nothing human foreign to me.
Heauton Timorumenos (The Self-Tormentor)

Das Schicksal des jüdischen Volkes ist das Schicksal Makbeths, der aus der Natur selbst trat, sich an fremde Wesen hing, und so in ihrem Dienste alles Heilige der menschlichen Natur zertreten und ermorden, von seinen Göttern (denn es waren Objekte, er war Knecht) endlich verlassen, und an seinem Glauben selbst zerschmettert werden mußte.
in Theologische Jugendschriften (1907), S. 261
The Spirit of Christianity and its Fate (1799)

"Quotes", The Educated Imagination (1963), Talk 2: The Singing School
Context: [L]iterature not only leads us toward the regaining of identity, but it also separates this state from its opposite, the world we don't like and want to get away from... We have to look at the figures of speech a writer uses, his images and symbols, to realize that underneath all the complexity of human life that uneasy stare at an alien nature is still haunting us, and the problem of surmounting it is still with us.... Literature is still doing the same job that mythology did earlier, but filling in its huge cloudy shapes with sharper lights and deeper shadows.

Living in Harmony (2000)

" The Buried Life http://www.victorianweb.org/authors/arnold/writings/buriedlife.html" (1852), st. 2
Context: Alas! is even love too weak
To unlock the heart, and let it speak?
Are even lovers powerless to reveal
To one another what indeed they feel?
I knew the mass of men conceal'd
Their thoughts, for fear that if reveal'd
They would by other men be met
With blank indifference, or with blame reproved;
I knew they lived and moved
Trick'd in disguises, alien to the rest
Of men, and alien to themselves — and yet
The same heart beats in every human breast!

Source: The Politics of Experience (1967), p. 3 of Introduction

The Wishing Tree (2015)

Source: Time is the Simplest Thing (1961), Chapter 32 (p. 249)