Dongshan Sick

KOAN:

When Dongshan was not feeling well, someone said, “Teacher, you are not feeling well. Is there anyone who doesn’t get sick?”
Dongshan said, “Yes, there is.”
“Does the person who doesn’t get sick take care of you?”
Dongshan said, “I have the opportunity to take care of the person.”
“What happens when you take care of that person?”
Dongshan said, “At that time, I don’t see the sickness.”