In Robert Loh’s book “Escape From Red China”, he relates how he communicated his despair to his father (living in Hong Kong). Because of censors, he could not express his thoughts directly…instead he quoted classical poets. I always remembered one passage “as long as the blue mountains stand, one need not doubt that trees will continue to grow”.
I never learned the source of this anyone know who the poet was?
I believe the phrase you are looking for is “留得青山在，不怕没柴烧”. It’s not really classical poetry, more of a vernacular saying.
Apparently the earliest place it appears in is Slapping the Table in Amazement (Chinese: 初刻拍案驚奇) a collection of short stories by Ling Mengchu published in 1627.