From The Asian Journal of Thomas Merton, a recording of of his 1968 trip to Bangkok, India, and Sri Lanka. This is a note from his Nov. 7 entry as he enjoyed a series of interviews with the Dalai Lama.
People who make no mental effort, even if they remain in mountain retreats, are like animals hibernating in their holes, only accumulating causes for a descent into hell.
The textual notes mark this as a Tibetan saying quoted by the Dalai Lama in his 1965 Introduction to Buddhism.
Extracts 