《北史·列传·卷七十七》
有个江南人叫祖日恒的，以前在边境上被俘获。住在王延明家，以前通晓算术历象，但不被王延明重用。
有江南人祖恆者，先于边境被获，在延明家，旧明算历，而不为王所待。
There was a Jiangnan native called Zu Ri Heng, who was previously captured at the border. He lived in Wang Yanming’s home and was knowledgeable about mathematics and astronomy but was not given much importance by Wang.