To not swear about the denial of money: To not swear about the disavowal, as it stated (Leviticus 19:11), “and you shall not lie” — meaning to say that if a man denied a deposit, he transgressed, “you shall not disavow”; and if he swore about the denial afterwards, he transgressed, “and you shall not lie.” As so has the understanding of this verse come to us, that it is to warn about one who swears about the denial of money. And [it is] like it appears in Sifra, Kedoshim, Section 2:3, “‘And you shall not lie’ — what do we learn to say? Since it is stated (Leviticus 5:22), ‘and he swears falsely,’ we have learned the punishment. From where is the warning? [Hence,] we learn to say, ‘and you shall not lie.’” And it is elucidated in Tractate Shevuot 49b that anyone who swears an oath about the denial of money, transgresses two negative commandments — on account of “And you shall not swear in My name falsely” (Leviticus 19:12), and on account of “and you shall not lie towards your compatriot.”

I have written in Parashat Vayishma Yitro in the commandment of “You shall not take” (Sefer HaChinukh 30) about the roots of the prohibition of a false oath.

And the laws of this commandment are in the fifth chapter of Shevuot.

And it is practiced in every place and at all times. And one who transgresses it and lies and volitionally takes an oath on his denial is lashed. And even though there is no act [involved] with it, the Torah made him liable for lashes, due to the weightiness of oaths.