Ekottaragama (Sanskrit fragments) 9.3.4

9.3.4

爾時，世尊告諸比丘：「我不見一法疾於心者，無譬可喻，猶如獼猴捨一取一，心不專定。心亦如是，前想、後想所不同者，以方便法不可摸則，心迴轉疾。是故，諸比丘！凡夫之人不能觀察心意。是故，諸比丘！常當降伏心意，令趣善道，亦當作是學。」

It was then that the Bhagavān addressed the monks, “I don’t see a single thing as quick as the mind. It cannot be grasped without using the method of the Dharma, and then the mind spins around quickly. Therefore, monks, ordinary people are unable to observe their mind thinking.

“Therefore, monks, one should control their thinking to lead their mind to the good path. Thus, monks, you should train yourselves.”