“I believe that it is possible for one to praise, without concern, any man after he is dead since every reason and supervision for adulation is lacking.”

Source: War and Peace

ibid

The Notebooks of Leonardo da Vinci (1883), XIX Philosophical Maxims. Morals. Polemics and Speculations.

The True Levellers Standard Advanced (1649)

Fragment 1.

Nul ne mérite d’être loué de bonté, s’il n’a pas la force d’être méchant: toute autre bonté n’est le plus souvent qu’une paresse ou une impuissance de la volonté.
Maxim 237.
Reflections; or Sentences and Moral Maxims (1665–1678)

Frost snorted. “I certainly do—if he has observed it with his own eyes and ears, or gets it from a source known to be credible. A fact doesn’t have to be understood to be true. Sure, any reasonable mind wants explanations, but it’s silly to reject facts that don’t fit your philosophy.”
Elsewhen (pp. 161-162)
Short fiction, Off the Main Sequence (2005)

In A Man Without a Country (2005) p. 80–81 Vonnegut makes a very similar statement:
God Bless You, Dr. Kevorkian (1999)
Context: About belief or lack of belief in an afterlife: Some of you may know that I am neither Christian nor Jewish nor Buddhist, nor a conventionally religious person of any sort.
I am a humanist, which means, in part, that I have tried to behave decently without any expectation of rewards or punishments after I'm dead. My German-American ancestors, the earliest of whom settled in our Middle West about the time of our Civil War, called themselves "Freethinkers," which is the same sort of thing. My great grandfather Clemens Vonnegut wrote, for example, "If what Jesus said was good, what can it matter whether he was God or not?"
I myself have written, "If it weren't for the message of mercy and pity in Jesus' Sermon on the Mount, I wouldn't want to be a human being. I would just as soon be a rattlesnake."

Source: The Way of Kings