《左传·僖公·僖公二十年》
凡是修筑城门和制作门闩，不应该妨碍农时。滑国人背叛郑国而顺服于卫国。
滑人叛郑而服于卫。
The construction of city gates and the manufacture of door bolts should not interfere with the farming season. The people of Hua betrayed Zheng and submitted to Wei.