We believe, according to the word of God, that the false and unnecessary use of an oath is an abomination before God.
Matthew 5:34-37 – But I say unto you, Swear not at all; neither by heaven; for it is God’s throne: Nor by the earth; for it is his footstool: neither by Jerusalem; for it is the city of the great King. Neither shalt thou swear by thy head, because thou canst not make one hair white or black. But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil. 
James 5:12 – 
But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation.

Ordinarily the language of the true believer is, “Yes, yes; no, no.” Nevertheless, the required oath in agreement with the gospel, calling upon God as a witness that the spoken word is the truth, is sanctioned by God. Thoughts from the Mount of Blessing, pp. 66, 67.
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; 
Deuteronomy 6:13
 – Thou shalt fear the LORD thy God, and serve him, and shalt swear by his name.