As milk, is evil kamma done,
so slowly does it sour.
Smouldering does it follow the fool
like fire with ashes covered.
~Dhammapada

Explanation: When an ignorance person commits an act of sin, it does not immediately yield bad results. This is like the freshly extracted milk, which does not curdle immediately on being extracted from the cow’s udder. The sin that has been committed remains concealed like the sparks covered with ashes, and continues to follow and burn the doer of sins. Source: Buddhanet