What is required in the ninth commandment?

Answer

The ninth commandment requires the maintaining and promoting of truth between man and man (), and of our own (; ) and our neighbour's good name (), especially in witness-bearing ().

Read the 5 proof texts (KJV)

Zechariah 8:16: These [are] the things that ye shall do; Speak ye every man the truth to his neighbour; execute the judgment of truth and peace in your gates:
1 Peter 3:16: Having a good conscience; that, whereas they speak evil of you, as of evildoers, they may be ashamed that falsely accuse your good conversation in Christ.
Acts 25:10: Then said Paul, I stand at Caesar's judgment seat, where I ought to be judged: to the Jews have I done no wrong, as thou very well knowest.
2 John 1:12: Having many things to write unto you, I would not [write] with paper and ink: but I trust to come unto you, and speak face to face, that our joy may be full.
Proverbs 14:5,25: ⁵A faithful witness will not lie: but a false witness will utter lies. ²⁵A true witness delivereth souls: but a deceitful [witness] speaketh lies.