Guan Yu is injured with a poison arrow, but shows no sign of pain as the wound is operated on

At the sight of Guan Yu falling from his charger, Cao Ren led his army out of the city to follow up with an attack, but Guan Ping drove him off and escorted his father back to camp. There the arrow was extracted, but the arrow head had been poisoned. The wound was deep, and the poison had penetrated to the bone. The right arm was discolored and swollen and useless.
Guan Ping consulted with the other leaders and proposed, saying, "As fighting is impossible for the moment, we should withdraw to Jingzhou, where my father's wound can be treated."

Having decided upon this, they went to see the wounded warrior.

...

Taking with him the other generals, Guan Ping went in to see his father. Guan Yu was engaging in a game of chess with Ma Liang, although his arm was very painful. But Guan Yu kept up appearances so as not to discourage the troops. When they told him that a physician had come, he consented to see him.

Hua Tuo was introduced, asked to take a seat and, after the tea of ceremony, was shown the injured arm.

"This was caused by an arrow," said the doctor. "There is poison in the wound, and it has penetrated to the bone. Unless the wound is soon treated, the arm will become useless."

"What do you propose to do?" asked Guan Yu.

"I know how to cure the wound, but I think you will be afraid of the remedy."

"Am I likely to be afraid of that when I am not even afraid of death? Death is only a return home after all."

Then Hua Tuo said, "This is what I shall do. In a private room I shall erect a post with a steel ring attached. I shall ask you, Sir, to insert your arm in the ring, and I shall bind it firmly to the post. Then I shall cover your head with a quilt so that you cannot see, and with a scalpel I shall open up the flesh right down to the bone. Then I shall scrape away the poison. This done, I shall dress the wound with a certain preparation, sew it up with a thread, and there will be no further trouble. But I think you may quail at the severity of the treatment."

Guan Yu smiled.

"It all sounds easy enough," said he. "But why the post and the ring?"

Refreshments were then served, and after a few cups of wine, the warrior extended his arm for the operation. With his other hand he went on with his game of chess. Meanwhile the surgeon prepared his knife and called a lad to hold a basin beneath the limb.

"I am just going to cut. Do not start," said Hua Tuo.

"When I consented to undergo the treatment, did you think I was afraid of pain?"

The surgeon then performed the operation as he had pre-described. He found the bone much discolored, but he scraped it clean. When the knife went over the surface of the bone and made horrible sounds, all those near covered their eyes and turned pale. But Guan Yu went on with his game, only drinking a cup of wine now and again, and his face betrayed no sign of pain.

When the wound had been cleansed, sewn up and dressed, the patient stood up smiling and said, "This arm is now as good as it ever was. There is no pain. Indeed, Master, you are a marvel."

"I have spent my life in the art," said Hua Tuo, "but I have never seen such a patient as you, Sir. You are as if not from the earth but heaven" (Romance of the Three Kingdoms, Ch 75).