“Let the apologists for communists acknowledge the dead, bury the dead, and atone for the dead. Otherwise, let them be forgiven only when they have put out their eyes and wandered blind, away from Thebes.”

Fragment iv.
Golden Sayings of Epictetus, Fragments

Source: Break-Out from the Crystal Palace (1974), p. 98

St. 6.
A Psalm of Life (1839)

I, st. 4
The Winding Stair and Other Poems (1933), A Dialogue of Self and Soul http://poetry.poetryx.com/poems/1397/
Context: My Soul. Such fullness in that quarter overflows
And falls into the basin of the mind
That man is stricken deaf and dumb and blind,
For intellect no longer knows
Is from the Ought, or knower from the Known —
That is to say, ascends to Heaven;
Only the dead can be forgiven;
But when I think of that my tongue's a stone.

Source: War and Peace

"Death"
Collected Poems 1921-1931 (1934)

Source: The Titan's Curse

In the 1880s, as quoted on an inscription at Vicksburg National Military Park http://jeffreyevanbrooks.blogspot.com/2015/09/sadness-and-hope-along-siege-lines-of.html.
1880s

John Rivers in The Genius and the Goddess (1955)
Context: You can't worship a spirit in spirit, unless you do it now. Wallowing in the past may be good literature. As wisdom, it's hopeless. Time Regained is Paradise Lost, and Time Lost is Paradise Regained. Let the dead bury their dead. If you want to live at every moment as it presents itself, you've got to die to every other moment.