“Wearily have the years passed, I know; wearily to the pale watcher on the hill who has been so long gazing for the daybreak; wearily to the anxious multitudes who have been waiting for his tidings below. Often has the cry gone up through the darkness, " Watcher, what of the night?" and often has the disappointing answer come, "It is night still; here the stars are clear above me, but they shine afar, and yonder the clouds lower heavily, and the sad night winds blow." But the time shall come, and perhaps sooner than we look for it, when the countenance of that pale watcher shall gather into intenser expectancy, and when the challenge shall be given, with the hopefulness of a nearer vision, "Watcher, what of the night?" and the answer will come, "The darkness is not so dense as it was; there are faint streaks on the horizon's verge; mist is in the valleys, but there is a radiance on the distant hill. It comes nearer — that promise of the day. The clouds roll rapidly away, and they are fringed with amber and gold. It is, it is the blest sunlight that I feel around me — Morning! It is Morning!"”

Chi alloggia alia prima osteria in ch’ ei avviene, trova ben spesso la mala notte.
La Veglia. (Ed. Milan, 1812. Opere, Vol. XIV., p. 223).
Translation reported in Harbottle's Dictionary of quotations French and Italian (1904), p. 261.

1950s
Source: Montgomery Bus Boycott speech, at Holt Street Baptist Church (5 December 1955) http://www.blackpast.org/?q=1955-martin-luther-king-jr-montgomery-bus-boycott

1960s, Beyond Vietnam: A Time to Break Silence (1967)
Context: Even when pressed by the demands of inner truth, men do not easily assume the task of opposing their government's policy, especially in time of war. Nor does the human spirit move without great difficulty against all the apathy of conformist thought within one's own bosom and in the surrounding world. Moreover, when the issues at hand seem as perplexing as they often do in the case of this dreadful conflict, we are always on the verge of being mesmerized by uncertainty; but we must move on.
And some of us who have already begun to break the silence of the night have found that the calling to speak is often a vocation of agony, but we must speak. We must speak with all the humility that is appropriate to our limited vision, but we must speak.
Context: Even when pressed by the demands of inner truth, men do not easily assume the task of opposing their government's policy, especially in time of war. Nor does the human spirit move without great difficulty against all the apathy of conformist thought within one's own bosom and in the surrounding world. Moreover, when the issues at hand seem as perplexing, as they often do in the case of this dreadful conflict, we're always on the verge of being mesmerized by uncertainty. But we must move on. Some of us who have already begun to break the silence of the night have found that the calling to speak is often a vocation of agony. But we must speak. We must speak with all the humility that is appropriate to our limited vision, but we must speak. And we must rejoice as well, for in all our history there has never been such a monumental dissent during a war, by the American people.

Source: Night (1960)
Context: "Don't be deluded. Hitler has made it clear that he will annihilate all Jews before the clock strikes twelve."
I exploded:
"What do you care what he said? Would you want us to consider him a prophet?"
His cold eyes stared at me. At last, he said wearily:
"I have more faith in Hitler than in anyone else. He alone has kept his promises, all his promises, to the Jewish people."

Epitaph for his daughter, Olivia Susan Clemens (1896), this is actually a slight adaptation of the poem "Annette" by Robert Richardson; more details are available at "The Poem on Susy Clemens' Headstone" http://www.twainquotes.com/headstone.html
Misattributed

Source: Selected Poems

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 108.