Another violation of the 9th commandment is the breaking of a promise. When you promise to do something, this must be followed through. Otherwise you will have testified falsely by stating an intent and plan to act, yet not actually doing so.
In the Bible, there are several accounts that speak against false promises. In James 5:12 it is written: “But above all, my brothers, do not swear, either by heaven or by earth or by any other oath, but let your “yes” be yes and your “no” be no, so that you may not fall under condemnation.”
A similar account can be found in the book of Matthew. Matthew 5:33-37 reads: “Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, Do not take an oath at all, either by heaven, for it is the throne of God, or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. And do not take an oath by your head, for you cannot make one hair white or black. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.”
The passages above clearly state that it is better not to make a promise at all, rather than to promise something you are not completely sure of fulfilling. Saying “yes” to do something must always mean that you intend to do so, no matter what happens. Similarly, saying “no” or ensuring that you will not do something must mean that you will certainly not commit the forbidden act.