The 62nd prohibition is that we are forbidden to swear a sh'vuas shav (a vain oath).
The source of this commandment is G‑d's statement,1 "Do not take the name of G‑d your L‑rd in vain."
[A sh'vuas shav is] when one swears that something is the opposite of what it actually is;2 or that something exists, when in fact it cannot;3 or that he will violate a mitzvah of the Torah.4 So too if one swears to an obvious and undisputed fact, such as swearing to G‑d that anything which is slaughtered will die. This is also considered a sh'vuas shav.
The Mishneh says,5 "What is a sh'vuas shav? An oath which contradicts an obvious truth."
One who transgresses this prohibition intentionally is punished by lashes. If done unintentionally, he is exempt [from even bringing a sacrifice], as with many other prohibitions, as explained above.6
There — i.e., in tractate Sh'vuos — it is said that this is the sh'vuas shav for which one is lashed if done intentionally and exempt if done unintentionally. The details of this mitzvah are explained there.
