Numbers 30:2 (ESV) If a man vows a vow to the Lord, or swears an oath to bind himself by a pledge, he shall not break his word. He shall do according to all that proceeds out of his mouth.
Matthew 5:34-37 (ESV)
34 But I say to you, Do not take an oath at all, either by heaven, for it is the throne of God,
35 or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King.
36 And do not take an oath by your head, for you cannot make one hair white or black.
37 Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.
James 5:12 (ESV) 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.