整句为：信不由中，质无益也。明恕而行,要之以礼,虽无有质,谁能间之！
出处———《左传·隐公元年》

【译文】讲信用不是发自内心，即使有人质也是没有用的
.能懂得将心比心地办事，并用礼来约束，虽然没有人质，又有谁能离间他们呢？
典故：
这是《左传》描写隐公三年，周郑两国国君为维护各自的利益以交换儿子作为“诚信”，但是，由于各自目的使然，最终“撕票”的故事。说的是：诚信如果不是出自内心，单凭交换人质是无益的。心地光明，互相了解；宽厚相待，彼此体谅，照这种精神行事，再以礼义相约，纵然没有人质，也可以实现“诚信”的目的！

Credit based on hostage exchange instead of good faith resulted in vain.If king Zhou and King Zheng know their own limits as well as those of the other and both parties observe the proprieties, even if there is no hostage, who can set them at loggerheads?

则，信不由中,质无益也.明恕而行,要之以礼得出的启示
The Hint on ‘Credit based on hostage exchange instead of good faith resulted in vain.’
or The Hint On the Story of Hostage Exchange for Credit in Spring and Autumn Period

供参考