Chapter 14: The Two Monkey Kings
The four of them were traveling when suddenly a monkey appeared who looked exactly like Sun Wukong. This fake Sun Wukong knocked out Tang Sanzang and stole the luggage. He even went before the Buddha to frame the real Sun Wukong.
The real Sun Wukong was very angry and fought with the fake Sun Wukong for three hundred rounds, but they could not tell who would win. They went to the Heavenly Court and asked the Jade Emperor to distinguish between true and false. The Jade Emperor asked the Pagoda-Bearing Heavenly King Li to use the Demon-Reflecting Mirror, but the mirror could not tell the difference either.
They then went before Guanyin, but she could not tell the difference either. Finally, they came before the Tathagata Buddha. The Buddha looked with his wisdom eye and immediately recognized the fake Sun Wukong. It turned out to be a six-eared macaque, and the Buddha subdued him. The real Sun Wukong finally cleared his name.