When you are thinking about an object, it sometimes occurs that evil, unwholesome thoughts connected with hate and delusion come into your mind. The way to get rid of them is to concentrate on another object that is wholesome and good. Just as a skilled carpenter knocks out a coarse peg with a fine one, so the evil thoughts will disappear. With their departure, the mind will become calm, unified, and concentrated once more.
- Majjhima Nikaya