Exodus 20:7

לשוא IN VAIN — for no valid reason, idly. What is a שבועת שוא, an oath taken for no valid reason? If one takes an oath declaring something, the nature of which is evident, to be different from what it is: e. g., swearing about a stone pillar that it is of gold (Shevuot 29a).

לֹ֥א תִשָּׂ֛א אֶת־שֵֽׁם־יְהֹוָ֥ה אֱלֹהֶ֖יךָ לַשָּׁ֑וְא כִּ֣י לֹ֤א יְנַקֶּה֙ יְהֹוָ֔ה אֵ֛ת אֲשֶׁר־יִשָּׂ֥א אֶת־שְׁמ֖וֹ לַשָּֽׁוְא׃ {פ}

Thou shalt not take the name of the Lord thy God in vain; for the Lord will not hold him guiltless that takes his name in vain.