Q: Which is the ninth commandment?
A: The ninth commandment is, Thou shalt not bear false witness against thy neighbour.
Q: What is required in the ninth commandment?
A: The ninth commandment requireth the maintaining and promoting of truth between man and man, and of our own and our neighbour’s good name, especially in witness bearing.
Q: What is forbidden in the ninth commandment?
A: The ninth commandment forbiddeth whatsoever is prejudicial to truth, or injurious to our own, or our neighbour’s good name.
(Questions LXXVI, LXXVII and LXXVIII from the Westminster Shorter Catechism.)