Looks like it is from "孫子兵法(The Art of War)"
其用戰也勝,久則鈍兵挫銳,攻城則力屈,久暴師則國用不足。夫鈍兵挫銳,屈力殫貨,則諸侯乘其弊而起,雖有智者不能善其後矣。故兵聞拙速,未睹巧之久也。夫兵久而國利者,未之有也。故不盡知用兵之害者,則不能盡知用兵之利也。
Here is a translation I found from the internet.
其用戰也,勝久則鈍兵挫銳,攻城則力屈,
When you engage in actual fighting, if victory is long in coming, then men's weapons will grow dull and their ardor will be damped. If you lay siege to a town, you will exhaust your strength.
久暴師則國用不足。
Again, if the campaign is protracted, the resources of the State will not be equal to the strain.
夫鈍兵挫銳,屈力殫貨,則諸侯乘其弊而起,雖有智者不能善其後矣。
Now, when your weapons are dulled, your ardor damped, your strength exhausted and your treasure spent, other chieftains will spring up to take advantage of your extremity. Then no man, however wise, will be able to avert the consequences that must ensue.
故兵聞拙速,未睹巧之久也。
Thus, though we have heard of stupid haste in war, cleverness has never been seen associated with long delays.
夫兵久而國利者,未之有也。
There is no instance of a country having benefited from prolonged warfare.
故不盡知用兵之害者,則不能盡知用兵之利也。
It is only one who is thoroughly acquainted with the evils of war that can thoroughly understand the profitable way of carrying it on.