Samyuktagama (Sanskrit fragments) 267.8

267.8

佛告比丘：「如嗟蘭那鳥種種雜色，我說彼心種種雜亦復如是。所以者何？彼嗟蘭那鳥心種種故其色種種。是故，當善觀察思惟於心，長夜種種貪欲、瞋恚、愚癡所染，心惱故眾生惱，心淨故眾生淨。

The Buddha told the monks, “I say that cāraṇa bird has diverse and varied colors because its mind is diverse and varied, too. Why is that? Because its mind is diverse, that cāraṇa bird’s color is diverse. Therefore, you should examine and contemplate the mind well, for it has been affected by diverse greeds, hatreds, and delusions for a long night. Sentient beings are troubled because their minds are troubled, and sentient beings are purified because their minds are purified.