许下 / 遵守 + 诺言
诺言 (nuòyán) is a noun meaning "a promise" or "a pledge," typically used in somewhat formal or literary contexts. Common collocations include 许下诺言 (to make a promise) and 遵守诺言 (to keep a promise). It carries a weightier, more solemn tone than the everyday verb 答应 (to promise).
他许下了诺言,一定会回来。
Tā xǔxiàle nuòyán, yīdìng huì huílái.
He made a promise that he would definitely come back.
做人要遵守自己的诺言。
Zuòrén yào zūnshǒu zìjǐ de nuòyán.
One should keep one's promises.
她从不轻易许下诺言,但说到就做到。
Tā cóng bù qīngyì xǔxià nuòyán, dàn shuō dào jiù zuò dào.
She never makes promises lightly, but always keeps her word.