《后汉书·列传·冯岑贾列传》
大司马刘秀在河北，他必定能用，只要持我的手书前往。 贾复于是辞别刘嘉，接受刘嘉书信北渡黄河，追及光武于柏人，由邓禹引见光武。
大司马刘公在河北，必能相施，第持我书往。 复遂辞嘉，受书北度河，及光武于柏人，因邓禹得召见。
Grand Marshal Liu Xiu is in Hebei. He will definitely employ you if you take my letter to him." Jia Fu then bid farewell to Emperor Liu Jia, accepted his letter, and crossed the Yellow River north. He caught up to Emperor Guangwu at Boren, and Deng Yu introduced him to Emperor Guangwu.