2,624. The Second and Third Subcategories of an Oath in Vain

Hilchos Shevuos 1:5

The second subcategory of an oath in vain is taking an oath about a known matter on which no one has a doubt, such as that the sky is the sky, that a stone is a stone, that two things are two, etc. Even though no mentally competent person has any doubts about this matter, one takes an oath to reinforce it.

Hilchos Shevuos 1:6

The third subcategory is taking an oath to nullify a mitzvah, such as if one took an oath not to wear tzitzis, not to put on tefillin, not to dwell in a succah on Succos, not to eat matzah on the first night of Passover, to fast on Shabbos and yom tov, and similar such cases.