《旧唐书·列传·卷一百一十六》
正当此时，足下兴致未尽，还打算与我一同收集友人唱和之诗，选取各自最佳之作，如张籍的古乐府，李绅的新歌行，卢拱、杨巨源二秘书郎的律诗，窦巩、元宗简的绝句，广搜精选，按序编排，取名《元白往还诗集》。
当此之时，足下兴有余力，且欲与仆悉索还往中诗，取其尤长者，如张十八古乐府，李二十新歌行，卢、杨二秘书律诗，窦七、元八绝句，博搜精掇，编而次之，号为《元白往还集》。
At that moment, you were all in the right mood, planning to gather together the poems we had exchanged with each other, and selected the best work of each of our friends, such as Zhang Ji's Music Bureau, Li Shen's New Ballad, the regulated poetry of the second assistant secretaries Lu Gong and Yang Juyuan, and the quatrain poems of Dou Gong and Yuan Zongjian, and carefully select and edit them, and arrange them in order, naming them Collected Poems Exchanged between Yuan and Bai.