《贞观政要·卷九·论安边》
黄河以西的百姓，是抵御强悍少数民族的前哨。那里人烟稀少，凋敝萧条，加之隋末的战火，老百姓遭受的损失尤其严重，在平定突厥之前，他们根本无法安居乐业，匈奴被削弱之后，才开始进行农业生产，如果现在就役使他们，恐怕会使他们元气大伤。臣固然愚钝，但还是请求陛下停止安抚劝降。
然河西民庶，镇御藩夷，州县萧条，户口鲜少，加因隋乱，减耗尤多，突厥未平之前，尚不安业，匈奴微弱以来，始就农亩，若即劳役，恐致防损，以臣愚惑，请停招慰。
The people west of the Yellow River are the outposts of resisting the strong ethnic minorities. There's a thin population there, a declining economy, and the wars of the late Sui Dynasty, so the people suffered especially heavy losses. Before the Turks were pacified, they could not live and work in peace. Only after the Huns were weakened did they start farming. If they are put into service now, I'm afraid it will hurt their vitality. Although I'm dull, I still ask Your Majesty to stop appeasement.