《资治通鉴·汉纪·汉纪五十三》
太尉杨彪认为黄河水路艰难，不宜于让天子冒这么大的危险。于是派李乐乘夜渡河，秘密准备船只，举火把作为信号。
杨彪以为河道险难，非万乘所宜乘；乃使李乐夜渡，潜具船，举火为应。
Minister Yang Biao thought the Yellow River was rough and dangerous, and it wouldn't be safe for the emperor to take the risk. So he ordered Li Le to cross the river in the night, secretly prepare the boat and light the torch as the signal.