One day after Yaoshan Weiyan had been seated in meditation for a long while, a monk asked him what he did during zazen: “What is it that you think of while you sit there as still as a mountain?”
“I think of not-thinking,” Weiyen replied.
“How can you think of not-thinking?” the bewildered monk persisted.
“It isn’t thought.”
[Yaoshan Weiyan – Zen Masters of China: 110-16]