《南史·列传·卷三十四》
文帝曾经分别下令让他们拟作乐府《北上篇》，颜延之受到诏令便作成了，谢灵运好久才写就。
文帝尝各敕拟乐府北上篇，延之受诏便成，灵运久之乃就。
Emperor Wen ordered them to compose <Poem of Northbound> for Le Fu, Yan Yanzhi created it right after receiving the order while Xie Lingyun took quite a while to finish his.