Nasai

(1) One should not make vows (nadhar) or oaths (qasm) regarding these things; it is prohibited. And if someone does take an oath or make a vow concerning these things, it should not be fulfilled, because a prohibited act cannot become permissible through a vow or oath. However, there is a difference of opinion regarding the expiation (kaffarah) for such an oath. The more correct view appears to be that expiation must be given, because this serves as a punishment for having used the exalted and sacred name of Allah in connection with something that is religiously prohibited. It is as if he has shown disrespect to the name of Allah; therefore, the meaning of vows and oaths not being valid in these matters is that, even with a vow or oath, the act will not become permissible. Rather, it is obligatory to break such a vow or oath, and he must pay expiation for this mistake. Some scholars are of the opinion that such a vow or oath does not even take effect, and therefore there is no need for expiation, but this view appears to be weak.

(2) It is permissible to make a vow (nadhar) regarding permissible (mubah) things; it is not permissible to make a vow in disobedience to Allah (ma‘siyat).

No one else can sell another person's property. If someone does sell it, such a sale will not be valid; the item will remain the property of the original owner. Therefore, the buyer should make sure before purchasing that the seller is indeed the actual owner; otherwise, the buyer's money may be lost because the item will go to the original owner. If the buyer is able to recover the money from the seller, then so be it; otherwise, it is lost, because the original owner cannot be asked to return the money.

Explanation:
1:
In some manuscripts, it is written with the accusative "seen" (س), i.e., "mansubah," and this is correct. By this is meant a woman who is attributed to a particular tribe or city, or "mansubah" may refer to a specific, designated woman.
For example, if someone says regarding a particular woman to whom he is not yet married, "If I marry such-and-such woman, then she is divorced," then after the marriage, divorce will take effect upon her,
even though at the present moment, this divorce is not within his ownership.

2:
For example, if he says, "If I marry today or tomorrow" (i.e., if I marry today or if I marry tomorrow).

Benefits and Issues:
In this narration, the portion from (man khalf 'ala yameen) to the end is weak.
(Shaykh al-Albani) And if one abandons the action upon which he has sworn an oath, then giving expiation (kaffarah) is preferable (rajih).

Takhrij:
«أخرجه أبوداود، الطلاق، باب في الطلاق قبل النكاح، حديث:2190، والترمذي، الطلاق واللعان، حديث:1181.»©Explanation:
➊ From this hadith, it is understood that for a person to exercise proprietary rights over something he does not own is meaningless. The exercise of such rights is unacceptable.
➋ This hadith is evidence that divorce does not take effect upon a non-mahram (unrelated) woman. For example: if a man says to another man's wife or to a woman who is not married to him, "You are divorced," and later on, that same man marries that woman, the scholars are unanimous that the woman will not be considered divorced. However, if someone says to a woman, "If I marry you, you are divorced," then regarding this situation, the scholars and jurists have three opinions:
• Imam Shafi'i, Imam Ahmad, Dawud al-Zahiri (rahimahumullah), and some other scholars are of the view that such a woman will not be considered divorced. Imam Bukhari (rahimahullah) has transmitted this opinion from twenty-two Companions (radi Allahu anhum), and the greatest evidence for this is this very hadith.
• The opinion of Imam Abu Hanifah (rahimahullah) is that such a woman will become divorced.
• The third opinion, held by Imam Malik (rahimahullah) and others, is that if someone specifies a woman from a particular tribe or city, or specifies a particular day or month, then in that case, divorce will take effect; but if he says it in a general sense, it will not take effect.
The ruling regarding freeing a slave and making a vow (nazr) is similar.
Among these opinions, the one closest to correctness is the first opinion, as has already been mentioned.