“I told you before, we’re the center,” she said. “And the center will hold.”

Source: The Collected Poems of W.B. Yeats

Black Elk Speaks (1961)
Context: To the center of the world you have taken me and showed the goodness and the beauty and the strangeness of the greening earth, the only mother — and there the spirit shapes of things, as they should be, you have shown to me and I have seen. At the center of this sacred hoop, you have said that I should make the tree to bloom.
With tears running, O Great Spirit, Great Spirit, my Grandfather — with running tears I must say now that the tree has never bloomed. A pitiful old man, you see me here, and I have fallen away and have done nothing. Here at the center of the world, where you took me when I was young and taught me; here, old, I stand, and the tree is withered, Grandfather, my Grandfather!
Again, and maybe the last time on this earth, I recall the great vision you sent me. It may be that some little root of the sacred tree still lives. Nourish it then, that it may leaf and bloom and fill with singing birds. Hear me, not for myself, but for my people; I am old. Hear me that they may once more go back into the sacred hoop and find the good red road, the shielding tree!

This is a paraphrase of lines in "The Second Coming" by William Butler Yeats.
Misattributed

Source: Mother of Storms (1994), p. 54

Source: The Viscount Who Loved Me

Source: Living on Luck

[2012, Echoes of Perennial Wisdom, World Wisdom, 7, 978-1-93659700-0]
Spiritual life, Happiness

BBC radio interview, The Listener (London, 1969-05-22)
General sources