《元史·本纪·卷七》
诸侯王派遣使者索取各种物品和驿马之类的事，从今以后都凭官府的公文，不能够只凭口信传达的命令。 
诸王遣使取索诸物及铺马等事，自今并以文移，毋得口传教令。 
From now on, princes delivering messengers to ask for various items and postal horses shall submit official documents from the government, rather than simply verbal orders.