《资治通鉴·唐纪·唐纪五十五》
在此之前，公主下嫁，都是选取皇家内外亲族以及功臣家的子弟。至此，宪宗才命令宰相选择公卿、大夫家的温文尔雅、可以置身清流的子弟。然而，各家多不愿意，只有杜佑的孙子司议郎杜没有推辞。
先是尚主皆取贵戚及勋臣之家，上始命宰相选公卿、大夫子弟文雅可居清贯者，诸家多不愿，惟杜佑孙司议郎悰不辞。
Before this, when the princess married, the children of the royal family, relatives, and meritorious ministers were selected. Therefore, Emperor Xianzong ordered the prime minister to select the children of the ministers and officials who were gentle and elegant, and who could stay away from the mundane. However, many families were reluctant, only Du You's grandson, Si Yilang Du, did not refuse.