A crow is never whiter for washing itself often

Question

There is a proverb in my language which says: "Finally, a wolf's cub, would be grow up as a wolf, although it is rised along with a human being." For more clarification, please consider the following story:

• It was a winter morning. Cold wind was blowing heavily. A farmer was going to his field. He found a snake half dead with cold, laying by the side of the road. He took pity on the of the road. He took pity on the wretched snake. He put it in his basket and brought it home. He warmed the snake with fire and gave it warm milk and made it fresh. It was all right with it and it got quite well very soon. It began to play with the children of the farmer. For the time being, it behaved well but afterwards it showed its actual behaviour and forgot the sympathy of the kind farmer. One day while playing with the children of the farmer, it spread out its fang and bit one of them. The farmer realised his mistake. He understood that an evil always remains an evil. So he became very angry and killed the snake with a stick, saying: ...................

I need to discover whether there is an equivalent for this proverb in English or not so that it could work in my story too and fill in the blank!

I have found a similar saying which I'm not confident about its origin and its prevalance among the people of the English spoken countries!

"a crow is never whiter for washing itself often"

Please help me to find the closest English equivalent for this comcept!

Answer 1

A leopard never changes its spots

This is more often used about adults really but:

something you say that means a person's character, especially if it is bad, will not change, even if they pretend that it will

https://dictionary.cambridge.org/dictionary/english/a-leopard-can-t-doesn-t-change-its-spots

Answer 2

Probably the most common saying about the immutability of essential natures comes from the Bible, at Jeremiah 13:23, which reads

Can the Ethiopian change his skin, or the leopard his spots? then may ye also do good, that are accustomed to do evil.

in the King James Version. (The Wycliffe Bible translates it as diversities, but The Phrase Finder traces it to Johan Bale in 1546.

In everyday usage the proverb is rendered as a leopard doesn't change its spots or a leopard cannot change its spots, or a leopard never changes its spots. From there it has been cloned onto other animals, especially a tiger can't change its stripes or a zebra never changes its stripes— though the animal may not even matter:

Preceding Tame Impala on the main stage, though, was Weezer, a band that couldn’t really change its stripes if its life depended on it. (Chris Willman, "Coachella Day 2: Billie Eilish Triumphs; Tame Impala and Weezer Bring the Rock," Variety, April 14, 2019)

Indeed, because the phrase has become a cliché with many variations, the metaphor is often mixed, sometimes deliberately for humorous effect:

They may be Wolves, but as the saying goes: a leopard can’t change its stripes. ("Predictions for Chelsea at Wolves: Put on some coffee, you might need it," The Pride of London, 5 December 2018)

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Another saying You can take the boy out of the country, but you can't take the country out of the boy. This has a slightly different meaning, that a person's upbringing is always evident even if you remove him or her to a different setting. This can be used both as a statement of pride in one's origin (and not forgetting your "roots") or as one of disparagement. The EL&U question traces it to the U.S. in the early 20th century;

This, too, has become a cliché and is endlessly snowcloned.

You can take the star out of Hollywood, but you can't take Hollywood out of the star. (Tina Daunt, "President-elect Barack Obama's inauguration tickets elude even Hollywood A-listers," Los Angeles Times, November 13, 2008)