Do not let your hearts be troubled by these defamatory
writings! Obey the words of Bahá’u’lláh and answer them not. Rejoice, rather,
that even these falsehoods will result in the spread of the truth. When these
slanders appear inquiries are made, and those who inquire are led into a
knowledge of the Faith.
If a man were to declare, ‘There is a lamp in the next room
which gives no light’, one hearer might be satisfied with his report, but a
wiser man goes into the room to judge for himself, and behold, when he finds
the light shining brilliantly in the lamp, he knows the truth! 
- ‘Abdu’l-Baha  (From a talk, Paris, November 20, 1911; ‘Paris Talks’)