[I]t is stated in the Nirvana Sūtra:

“Bodhisattvas, do not be afraid of such things as wild elephants, but fear ‘evil friends.’ Why? Because a wild elephant may destroy our bodies but not our minds, while an ‘evil friend’ can destroy both. A wild elephant may crush merely one person, but an ‘evil friend’ can crush both body and mind of innumerable persons. An elephant may crush merely an impure, stinking body, but an ‘evil friend’ can destroy both pure body and mind. A wild elephant may merely ruin our flesh and blood, while an ‘evil friend’ can corrupt our Buddha nature. Killed by a wild elephant, we may not fall into the three evil realms; however, it seems inevitable for us to fall there when we die of an ‘evil friend.’ This wild elephant is only a physical enemy, while this “evil friend” is the enemy of the True Dharma. You, Bodhisattvas, therefore, should always be careful to stay away from ‘evil friends’.”

Shugo Kokka-ron, Treatise on Protecting the Nation, Writings of Nichiren Shōnin, Doctrine 1, Pages 57-58