信以为真

信以為真
xìnyǐwéizhēn
to take sth to be true

CEDICT

to take (something) to be true

Wiktionary

相信是真的。

重編國語辭典

是假的事情，却被误认为是真的。

維基詞典

Entry Composition

1 信 xìn
  1. letter
  2. mail
  3. to trust
  4. to believe
  5. to profess faith in
  6. truthful
  7. confidence
  8. trust
  9. at will
  10. at random

classifier: 封
2 以为 yǐwéi to think; to believe (often with the implication that the belief is mistaken – unless referring to one's own current belief)
3 真 zhēn
  1. really
  2. truly
  3. indeed
  4. real
  5. true
  6. genuine