负荆请罪, to carry thorns and ask for punishment, comes from Sima Qian’s Records of the Grand Historian. General Lian Po of Zhao was angry that Lin Xiangru, a man of humble birth, had been given a higher rank, although Lian Po had won great merit in battle. He announced that he would humiliate Lin if he met him. Lin avoided him for the sake of the state.
When Lian Po learned why, he was ashamed. He went to Lin carrying thorns and asked to be punished. The two became friends who would die for each other.