The Qur'an has several verses that relate to the making of oaths. Some of the more important verses are:
And make not God's (name) an excuse in your oaths against doing good, or acting rightly, or making peace between persons; for God is One Who heareth and knoweth all things. (2:224)
God will not call you to account for thoughtlessness in your oaths, but for the intention in your hearts; and He is Oft-forgiving, Most Forbearing. (2:225)
God will not call you to account for what is futile in your oaths, but He will call you to account for your deliberate oaths: for expiation, feed ten indigent persons, on a scale of the average for the food of your families; or clothe them; or give a slave his freedom. If that is beyond your means, fast for three days. That is the expiation for the oaths ye have sworn. But keep to your oaths. Thus doth God make clear to you His signs, that ye may be grateful. (5:92)
Fulfill the Covenant of God when ye have entered into it, and break not your oaths after ye have confirmed them; indeed ye have made God your surety; for God knoweth all that ye do. (16:91)
As you can see, in Islam, the breaking of oaths has strong consequences so the making of an oath is an important matter to think over. For example,
For those who take an oath for abstention from their wives, a waiting for four months is ordained; if then they return, God is Oft-forgiving, Most Merciful. (2:226)
Deciding to separate from one's spouse automatically requires a four month period for both the cooling off of emotions and also to determine if the wife may have conceived a child.
The strong consequences also occur in any aspect where some sort of contract is drawn up, such as a business transaction, or in a legal proceeding:
But if it gets known that these two were guilty of the sin (of perjury), let two others stand forth in their places,- nearest in kin from among those who claim a lawful right: let them swear by God: "We affirm that our witness is truer than that of those two, and that we have not trespassed (beyond the truth): if we did, behold! the wrong be upon us!"
That is most suitable: that they may give the evidence in its true nature and shape, or else they would fear that other oaths would be taken after their oaths. But fear God, and listen (to His counsel): for God guideth not a rebellious people: (5:110-11)
Likewise, a dispute between husband and wife requires the strongest of oaths and a very terrible consequence if one of the two is lying against the other:
And for those who launch a charge against their spouses, and have (in support) no evidence but their own,- their solitary evidence (can be received) if they bear witness four times (with an oath) by God that they are solemnly telling the truth;
And the fifth (oath) (should be) that they solemnly invoke the curse of God on themselves if they tell a lie.
But it would avert the punishment from the wife, if she bears witness four times (with an oath) By God, that (her husband) is telling a lie;
And the fifth (oath) should be that she solemnly invokes the wrath of God on herself if (her accuser) is telling the truth. (24:6-9)
Finally, the following verse sums up very well both the consequences to breaking one's oath and the potential rewards, insha'allah, for keeping one. (This verse has an historical background to it, but the general application remains applicable.)
Verily those who plight their fealty to thee do no less than plight their fealty to God: the Hand of God is over their hands: then any one who violates his oath, does so to the harm of his own soul, and any one who fulfills what he has covenanted with God,- God will soon grant him a great Reward. (48:10)
Cross posted at Street Prophets.