首楞嚴義疏注經 2.636

2.636

類說應云：如是崖想，不從崖生，不從足入。若崖生者，崖合自思，何待人想？若從足入，足應有思，何須心想？若獨心思，此酸只應心中自有，何以足心却有酸澁？

By analogy with the speaking, one should say: such thought of the cliff does not arise from the cliff, nor does it enter from the feet. If it arose from the cliff, the cliff ought to think of itself; why wait for a person to think? If it entered from the feet, the feet ought to have thoughts; why need the mind to think? If the mind alone thinks, this sourness should only exist in the mind; why do the soles of the feet instead have sour astringency?