Matot 

מטות

Vows and oaths that a person utters are especially severe. Only people of great virtue are permitted to take an oath invoking the name of God, even if their statements are absolutely true. 

The Holy One, Blessed be He, said to Israel: Be very cautious concerning vows and do not become lax in their regard, as anyone who is lax concerning vows will ultimately take false oaths. And anyone who takes false oaths denies My existence, and he will never gain atonement, as it is stated: “As the Lord will not absolve one who takes His name in vain” (Exodus 20:7)…. The Holy One, Blessed be He, said to Israel: Do not think that it is permitted for you to take an oath in My name. You are not permitted to take an oath in My name even in truth unless you have all these attributes: “The Lord your God you shall fear, Him you shall serve, and to Him you shall cleave, and in His name you shall take an oath” (Deuteronomy 1:17). You must be like these three who were called God-fearing: Abraham, Job, and Joseph…. If you have all these attributes, you may take an oath, but if not, you may not take an oath.  <source>(<i>Tanĥuma</i>, <i>Matot</i>) </source>