Maleakhi 2:14

2:14 Yet you ask, “Why?” The Lord is testifying against you on behalf of the wife you married when you were young, ¹  to whom you have become unfaithful even though she is your companion and wife by law. ² 

[2:14]  ¹ tn Heb “the Lord is a witness between you and [between] the wife of your youth.”

[2:14]  ² sn Though there is no explicit reference to marriage vows in the OT (but see Job 7:13; Prov 2:17; Ezek 16:8), the term law (Heb “covenant”) here asserts that such vows or agreements must have existed. References to divorce documents (e.g., Deut 24:1-3; Jer 3:8) also presuppose the existence of marriage documents.