nourish a viper in (one's) bosom To befriend, look after, or take care of someone who proves to be traitorous, untrustworthy, deceitful, or ungrateful.

Perhaps a Russian speaker will know the exact sense of this aphorism. But can you explain it to help us?

Natalia is correct. I found reference to this statement from Aesop's Fables and Chaucer and later William Shakespear. The more common idiom taking the snake's perspective might be, "[don't] bite the hand that feeds you."