《隋书·列传·卷二十五》
他九岁时，曾在云阳宫拜见北周太祖。太祖问他： 听说你爱读书，书上有些什么？ 
年十五，周太祖见而异之，令与诸子同就学。
When he was nine years old, he once met the Emperor Taizu of the Northern Zhou Dynasty in the Yunyang Palace. Taizu asked him: "I heard that you love to read. What's in the books?"