Name the wrong
Invoking God’s name to give false words an appearance of sacred authority.
Commandment 3 · Honour God’s name

You promised a client that work was complete. It was not. When challenged, you say, “God knows I have done everything I said.” The phrase sounds solemn. It is also being used to protect a statement you know is false. Your religious language is lending weight to your own deception.
Thou shalt not take the name of the LORD thy God in vain; for the LORD will not hold him guiltless that taketh his name in vain.Exodus 20:7 · King James Version
Choose the response you are prepared to defend. Then examine the cost.
Invoking God’s name to give false words an appearance of sacred authority.
Speaking of God reverently and refusing to use His name as cover.
This command concerns God’s name. The dishonesty in the case makes its misuse especially plain.
Review a promise you have reinforced with religious language. Does the underlying conduct support the words? Correct one claim that does not.