This is a story from Three Kingdoms.
Zhou Yu, a strategist of the Wu Kingdom, was brilliant but also narrow-minded and jealous of those he deemed smarter. He harbored a deep desire to eliminate Zhuge Liang and Liu Bei of the rival Shu Kingdom.
One day, Zhou Yu invited Liu Bei to cross the river for a meeting, deliberately keeping it secret from Zhuge Liang, who was then in Wu as an ally. Delighted to see Liu Bei arrive, Zhou Yu had arranged for an assassin to kill him at the banquet. The signal for the attack was to be Zhou Yu throwing his cup to the ground.
Zhuge Liang was alarmed to discover Liu Bei's meeting with Zhou Yu. He rushed anxiously to the tent and was relieved to see Guan Yu standing guard behind Liu Bei. Satisfied with this protection, Zhuge Liang then retreated to a small boat by the river to await their return.
At the feast, after host and guest had enjoyed several rounds of wine, Zhou Yu stood up, cup in hand. Noticing the formidable warrior standing behind Liu Bei with his hand on his sword, Zhou Yu inquired about his identity. "This is my sworn brother, Guan Yunchang," Liu Bei replied. "Could he be the one who slew the renowned generals Yan Liang and Wen Chou?" Zhou Yu asked nervously. "The very same," Liu Bei confirmed. A chill ran down Zhou Yu's spine, and he broke into a cold sweat. He hastily poured a cup of wine for Lord Guan, drank with him, and remarked, "Your fame is well-earned, having slain six generals and breached five passes!"
When Liu Bei asked about Zhuge Liang's whereabouts, Zhou Yu suggested they meet again only after Cao Cao was defeated. Lord Guan exchanged a meaningful glance with Liu Bei, who understood the cue and immediately rose to take his leave. Zhou Yu, now thoroughly intimidated, made no attempt to stop them.
Upon reaching the riverbank, Liu Bei and Guan Yu were overjoyed to find Zhuge Liang waiting in his boat. "My lord," Zhuge Liang said, "You were in grave danger today, more than you realized. Were it not for Lord Guan's presence, Zhou Yu would certainly have killed you."