...if anyone utters with his lips a rash oath to do evil or to do good, any sort of rash oath that people swear, and it is hidden from him, when he comes to know it, and he realizes his guilt in any of these...
Leviticus 5:4

This is talking about accidental oaths and vows. "How is it possible to make an accidental or unknown oath" you ask?

Answer: Do you always read the details of every End User License Agreement? Do you always control your tongue in a moment of surprise or anger?