Positive commandment · Mitzvat Aseh #7 of 613
To swear in His name
לְהִשָּׁבַע בִּשְׁמוֹ
The verse · Devarim 10:20
אֶת־ה׳ אֱלֹהֶיךָ תִּירָא אֹתוֹ תַעֲבֹד וּבוֹ תִדְבָּק וּבִשְׁמוֹ תִּשָּׁבֵעַ
“Thou shalt fear the Lord thy God; him shalt thou serve, and to him shalt thou hold fast, and swear by his name.”
The Rambam’s words
To swear in His name, as [Deuteronomy 10:20] states: "And you shall swear in His name."
לְהִשָּׁבַע בִּשְׁמוֹ, שֶׁנֶּאֱמָר: "וּבִשְׁמוֹ, תִּשָּׁבֵעַ" (דברים ו יג, י כ).
Why · Sefer HaChinuch #435
To swear in His name, may He be blessed, truthfully
“It is from the roots of the commandment that in our establishing our words in His great name, the faith in Him and His supervision over us and over all our words are strengthened in our hearts.”
Who & when
“And it is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Oaths הלכות שבועות