Heidelberg Catechism · 1563

Q101. But may we swear an oath by the Name of God in a godly manner?

Yes, when the government demands it of its subjects, or when necessity requires it, in order to maintain and promote fidelity and truth, to God's glory and for our neighbour's good. Such oath-taking is based on God's Word and was therefore rightly used by saints in the Old and the New Testament.
Answer · Heidelberg Catechism

Scripture proofs

  1. [1]
    Deuteronomy 6:13

    Thou shalt fear the Lord thy God, and serve him, and shalt swear by his name.

    Deuteronomy 10:20

    Thou shalt fear the Lord thy God; him shalt thou serve, and to him shalt thou cleave, and swear by his name.

    Jeremiah 4:1-2

    If thou wilt return, O Israel, saith the Lord, return unto me: and if thou wilt put away thine abominations out of my sight, then shalt thou not remove. And thou shalt swear, The Lord liveth, in truth, in judgment, and in righteousness; and the nations shall bless themselves in him, and in him shall they glory.

    Hebrews 6:16

    For men verily swear by the greater: and an oath for confirmation is to them an end of all strife.

  2. [2]
    Genesis 21:24

    And Abraham said, I will swear.

    Genesis 31:53

    The God of Abraham, and the God of Nahor, the God of their father, judge betwixt us. And Jacob sware by the fear of his father Isaac.

    Joshua 9:15

    And Joshua made peace with them, and made a league with them, to let them live: and the princes of the congregation sware unto them.

    1 Samuel 24:22

    And David sware unto Saul. And Saul went home; but David and his men gat them up unto the hold.

    1 Kings 1:29-30

    And the king sware, and said, As the Lord liveth, that hath redeemed my soul out of all distress, Even as I sware unto thee by the Lord God of Israel, saying, Assuredly Solomon thy son shall reign after me, and he shall sit upon my throne in my stead; even so will I certainly do this day.

    Romans 1:9

    For God is my witness, whom I serve with my spirit in the gospel of his Son, that without ceasing I make mention of you always in my prayers;

    2 Corinthians 1:23

    Moreover I call God for a record upon my soul, that to spare you I came not as yet unto Corinth.

Proof texts as given in the original; verse text from the King James Version.