Promise to Be Truthful
Notaries Public often must place witnesses under an oath or affirmation in order for their actions and words to serve as evidence.
Prior to testimony, a witness might be asked...
"Do you solemnly swear (or affirm) under the penalties of perjury that the testimony you are about to give in this matter is the truth, the whole truth and nothing but the truth?"
The question to those who prefer an oath ends with "so help you God."