《新唐书·列传·卷一百二十六》
青年时与李峤、崔融、苏味道为文章四友，世人称为： 崔、李、苏、杜。 
少与李峤、崔融、苏味道为文章四友，世号 崔、李、苏、杜 。
In his youth, he was an intimate friend of Li Jiao, Cui Rong and Su Weidao, who were known as the Four Friends of Literature, and the world referred to them as Cui, Li, Su and Du.