《北史·列传·卷五十三》
管理库房的人告诉了晋公宇文护，宇文护因为他功高勋重，不便张扬他的过失，因而把金带赐给了他。人们议论起来都很鄙视他。蔡祐，字承先，祖先为陈留国人，后来徙居高平。他聪明敏捷，颇有道德。长大后臂力过人，宇文泰将他召至帐下当作亲信。
祐性聪敏，有行检。袭之背贼东归，祐年十四，事母以孝闻。及长，有膂力。周文在原州，召为帐下亲信。
The official who managed the treasury reported this matter to the Duke of Jin, Yuwen Hu. Since Yuwen Hu respected his weighty merits and outstanding achievement, he did not make his fault public. Thus, he granted him the golden belt. People all despised him in their discussions. Cai You, whose courtesy name was Chengxian, was originally from Chenliu Commandery, though his ancestors later migrated to Gaoping. He was intelligent and active, with considerable virtue. When he grew up, he possessed exceptional physical strength. Yuwen Tai summoned him to his camp to serve as a close associate.