Tongue

He must . . . observe silence and refrain from idle talk. For the tongue is a smoldering fire, and excess of speech a deadly poison. Material fire consumeth the body, whereas the fire of the tongue devoureth both heart and soul. The force of the former lasteth but for a time, whilst the effects of the latter endureth a century.

Bahá’u’lláh, Gleanings from the Writings of Bahá’u’lláh, p. 264