怪力亂神

From the Analects, Book 7 (《論語·述而》):

子不語：怪、力、亂、神。 [Traditional Chinese poetry, trad.]

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子不语：怪、力、乱、神。 [Traditional Chinese poetry, simp.]

From: The Analects of Confucius, c. 475 – 221 BCE, translated based on James Legge's version

Zǐ bù yǔ: guài, lì, luàn, shén. [Pinyin]

The subjects on which the Master did not talk, were — extraordinary things, feats of strength, disorder, and spiritual beings.

怪力亂神

1. (dated, literal) monstrousness, violence, rebellion and supernaturalism
2. (figurative) superstition

This idiom was originally to be comprehended character by character, but people nowadays split it by two two-character endocentric phrases, hence the "superstition" meaning.