At Cao Cao's instruction, Liu Bei was about to set off for a punitive（惩罚的） expedition against Yuan Shu. Before he left, Liu Bei worried about the defence of Xuzhou City. When Zhang Fei volunteered to take the task, Liu said, "How can I feel assured, when you're so fond of drinking and after drinking you always flog（鞭打） your soldiers for no reason? And you're such a hot-tempered person and frequently you refuse to take advice." He entrusted（委托） the task upon Zhang only after the latter's repeated entreatments and resolutions to mend his ways. For safety, he left consultant Chen Deng to assist Zhang.

One day Zhang invited his subordinate（下属，下级） officers over. "My elder brother instructed me before he left to stay away from wine for fear I may fail my duties to guard the city. Let's have an final drinking party today, and starting from tomorrow, we will quit drinking and concentrate on the job."

With these words said, he began toasting everyone. When neither of his toasts was accepted by Cao Bao, Zhang flared up. By then , Zhang was already drunk. He had Cao flogged fifty times.

After the party was over, the resentful Cao sent one of his men to Lv Bu, the enemy general, asking him to attack the city that night while Zhang was drunk. Lv came with 500 horsemen. They successfully took the city. When Zhang woke up with a start, the city was gone. He fought his way out of the enemy troops and fled the city, leaving his elder brother's family behind.

When he met Liu, he felt so shame-faced that he unsheathed（抽出鞘） his sword meaning to commit suicide, only to be stopped by his elder brother.