It is better not to make a vow than to make one and not fulfill it.
Read Ecclesiastes 5:5 Using Other Translations
Better is it that thou shouldest not vow, than that thou shouldest vow and not pay.
It is better that you should not vow than that you should vow and not pay.
It is better to say nothing than to make a promise and not keep it.
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(New International Version Bible Online)