Emperor Wen-tsung of the T'ang dynasty liked to eat clams. Fishermen along the coasts often sent gifts of clams to the Imperial Palace as tribute to the Emperor. Once, the cook found a figure that resembled Kuan-yin in a clam shell. Since it was such a vivid and solemn image, the emperor had it put in a treasure box inset with beautiful silk. It then was placed in Hsing-shan Temple for people to pay homage. Finding the figure of Kuan-yin in a clam was most unusual. Thus, the Emperor asked his officials, "Gentlemen, do any of you know what propitious omen the figure in the shell represents?"
One answered, "This is something beyond the understanding of worldly scholars. There is a Ch'an master, Yao-shan Wei-cheng, in T'ai-i Shan, who is well-versed in Buddhism. He also is possessed of broad learning and a phenomenal memory. If Your Majesty wants to find out the significance of the figure, you may have to send for him."
When the Master was called in, he told the Emperor, "Everything appears in response to something else. This figure is intended to strengthen your belief. The Lotus Sutra states that for those who should be saved by a bodhisattva, one would emerge to expound the Dharma to them in person. This is happening to you now, Your Majesty."
"Although the Bodhisattva has appeared, I haven't heard the explanation of the Dharma," said Wen-tsung.
"Do you think this sacred figure in the clam will inspire your belief, Your Majesty?" asked Master Wei-cheng.
"I have seen this unusual thing with my own eyes, and of course, I believe it," replied Emperor Wen-tsung.
"You owe this belief to Kuan-yin, who has expounded the Dharma to you by her appearance in the shell," declared the Master.
(Source: Hsing Yun's Ch'an Talk, Book 4)