《资治通鉴·唐纪·唐纪二十九》
唐玄宗从泰山封禅返回后，张说对他说： 吐蕃对我国无礼，确实应该讨伐平定它，但十余年接连打仗，甘、凉、河、鄯等地再也承受不住战争的祸害了，虽然出师屡屡获胜，但是得不偿失。
初，吐蕃自恃其强，致书用敌国礼，辞指悖慢，上意常怒之。返自东封，张说言于上曰： 吐蕃无礼，诚宜诛夷，但连兵十馀年，甘、凉、河、鄯、不胜其弊，虽师屡捷，所得不偿所亡。
After Emperor Xuanzong of Tang returned from his coronation at Mount Tai, Zhang Shuo told him: "Though the Tufan have been disrespectful towards my dynasty and should be subjugated, over a decade of continuous warfare has taken its toll on Gansu, Liangzhou, Hexi Corridor, and Shannan; though our forces have often been victorious, the cost has been too great.