The Wordings of Oaths and Swearing
Question :
Is the expression: "Yaminullah" (Allah's Oath) consid- ered to be swearing an oath? And likewise, when a woman says to another: "I will be guilty of committing a sin if you do such-and-such, or take such-and-such." And what is an emphatic oath? Advise me and may Allah bless you.
Answer:
If a person says: "Yameenullah" or something similar, then that is considered an oath, and it affirms what is affirmed by a clear oath beginning with the letter Waw or Ba or Ta.
Likewise, if a person declares something forbidden to himself, then this prohibition for himself carries the ruling of an oath, according to the Words of Allah, Most High:
"O Prophet! Why do you forbid (for yourself) that which Allah has allowed to you, seeking to please your wives? And Allah is Oft-Forgiving, Most Merciful. Allah has already ordained for you (O men) the absolution from your oaths. "
And the Words of Him, Most High:
"O you who believe! Make not unlawful the Tayyibat (all that is good as regards foods, things, deeds, beliefs, persons) which Allah has made lawful to you, and transgress not. Verily, Allah does not like the transgressors. And eat of the things which Allah has provided for you, lawful and good, and fear Allah in Whom you believe." Allah will not punish you for what is unintentional in your oaths, but He will punish you for your deliberate oaths."
So Allah has mentioned atonement after He prohibited us from declaring the good He has allowed us to be forbidden.
When a person declares something forbidden, it is as if he swore an oath not to do it. If he said: "It is forbidden to me to enter the house of so-and-so," it is the same as his saying: "By Allah, I will not enter the house of so-and-so." And if he said: "It is forbidden to me to sell this thing," it is the same as if he said:
"By Allah, I will not sell this thing." There is no difference in this according to the most authoritative view - between the prohibition of the woman, i.e., the wife or another, due to the generality of the evidences which prove that, i.e., declaring something forbidden is the same as swearing an oath.
As for an emphatic oath, its emphasis may be from a number of different means. The first is from the view of the wording. Such as when the wording is associated with the Names of Allah, the Almighty, the All-Powerful which prove the Punishment for one who contradicts them, such as: "Wallahil 'Azimullathi La Ilaha Illa Huwal-Qahhar" (By Allah, the Great, aside from Whom none is worthy of worship but He, the Irresistible) and other similar Names which prove His Irresistibility and His Punishment.
They may also be emphasized by time. Such as when it is after 'Asr, such as the Words of Allah, Most Blessed, Most High:
"Detain them both after As-Salat (the prayer), (then) if you are in doubt (about their truthfulness), let them both swear by Allah (saying)
The scholars said it may be emphasized by the place, such as when a person is at the pulpit of the Friday prayer. It may be emphasized by the position, such as when a person is standing, as it has been stated by some of the scholars may Allah have mercy on them.
The oath might be emphasized due to the consequence of it. Such as if it was stated to separate someone from his wealth, this type of emphatic oath is a false oath, according to the words of the Prophet ﷺ :
"Whoever swore to an oath in which he lies, acquiring the wealth of a Muslim person, will meet Allah and He will be Angry with him."
Source:
Ibn Uthaimin
Fatawa Islamiyah, Vol. 6 Pages 364-365-366