My friend recently took an oath on her dead grandmother an later we discovered she was lying; I want to know what would happen?
assalaamu 3alaykum wa ra7matullahi wa barakaatuh
I do not know whether your question is related to someone taking an oat by the grave of someone ( i.e. saying: By the grave of my grandmother I will do this and this... ) or if you ask when someone gave an oath to someone before the person died. But I will in shaa Allah answer on both issues and you see whether the answer suffices you, else in shaa Allah clarify it more.
Swearing by anything other than Allah is not permissible. Rather the oath should be by Allah alone, may He be glorified and exalted, because it is proven that the Messenger of Allah (blessings and peace of Allah be upon him) said:
“Whoever swears an oath, let him not swear by anything except by Allah, or else let him remain silent.”
and he also said:
“Whoever swears by anything other than Allah has associated something with Him (shirk).”
so it is not permissabe to make an oath by other than Allah. If someone made any such oath then this is not an oath since it is haram to make such oaths.
Regarding the second issue I mentioned that someone makes an oath to someone before the person dies there are 2 issues:
1) is the action the person swore to do halal or haram ( if it is haram then there is no oath because you can not do something against Allah )
2) what to do in case of making an oath and breaking it ( based on actions that are halal )
The first situation is clear because you can not go against Allah 'azza wa jalla and one should never make an oath like this, for example: by Allah if you do not give me this I will not do my salah, this is a sin and should be left
The second situation is something else,
al-Bukhaari (6718) and Muslim (1649) report from Abu Moosa al-Ash‘ari (may Allah be pleased with him), according to which the Prophet (blessings and peace of Allah be upon him) said: “By Allaah, if Allaah wills, I do not swear an oath then see something better than that, but I expiate my oath and do that which is better.”
Muslim (1650) narrated that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever swears an oath then sees that something else is better than it, let him do that and offer expiation for his oath.”
The expiation for breaking an oath is to set free a slave, or to feed or clothe ten poor persons. Whoever cannot do any of those things should fast for three days, because Allaah says:
“Allaah will not punish you for what is unintentional in your oaths, but He will punish you for your deliberate oaths; for its expiation (a deliberate oath) feed ten Masaakeen (poor persons), on a scale of the average of that with which you feed your own families, or clothe them or manumit a slave. But whosoever cannot afford (that), then he should fast for three days. That is the expiation for the oaths when you have sworn. And protect your oaths (i.e. do not swear much). Thus Allaah makes clear to you His Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) that you may be grateful”
If the person does not care about it then the person has comitted a sin and should repent to Allah and make the expiation for breaking valid oath and if the person doesn't do any of these then 'everyone will have what they have earned'.
I hope this clarified a few things in shaa Allah wa Allahu ta3aalaa a3lam
Baarak Allah feekum