An Oath to Donate
4-4-2018 | IslamWeb
Question:
Salamuaalaikum as Rahmatu Allah wa barakatu, I made an oath by swearing in my prayer to Allah that I would never ever do a certain thing (a certain sin) again and that I would donate 10000 € if I will do it again. Despite that I did the sin again. I read that the expiration for breaking an oath is to feed 10 poor people. Do I have to feed the ten people for breaking my oath or do I have to fullfill the actual oath by donating 10000€. Technically I am able to donate the 10000 € since I have it on my account but if I have to pay it, is it permissible to pay it in monthly rates since its hard to spend that much many at once, even though I have the amount right now?
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
First of all, making an oath while you are in prayer is considered as speaking, and the prayer is invalidated by speaking.
Ash-Shawkaani said in Nayl Al-Awtaar:
"There is no difference of opinion among the scholars that whoever deliberately speaks during the prayer while knowing that he is prohibited from doing so, then his prayer is void. Ibn Al-Munthir said: 'The scholars agreed that whoever deliberately speaks in his prayer while it is not for the benefit of the prayer (like if the Imaam makes a mistakes and does not realize what is wrong), then his prayer is void. However, they differed in opinion about someone who speaks out of forgetfulness or out of ignorance (not knowing the ruling of speaking).' At-Tirmithi reported that most scholars are of the view that it is the same whether the person speaks out of forgetfulness, or ignorance, or deliberately…..” [End of quote]
The view we adopt here in Islamweb is that speaking during the prayer out of forgetfulness does not invalidate the prayer. But, in order to be on the safe side, it is better to repeat it.
Nonetheless, you have to repent to Allah because of committing that sin and because of breaking your oath, because whoever makes an oath to abandon what is forbidden, it is forbidden for him to break his oath.
The Fiqh Encyclopedia reads:
"An oath to do an obligation or to abandon a sin, such as saying: ‘I swear by Allah that I will surely pray Thuhr today’, or ‘I will not steal tonight’; it is an obligation to fulfill this oath and it is forbidden to break it, and there is no difference of opinion about this as it is known.” [End of quote]
Your saying "I would donate 10,000 € if I will do it (sin) again”; is either of the two following cases:
1- You had intended an oath and not a vow: this is another oath for donating the amount if you commit the sin again. In which case, since you dared to commit the sin, then you should take the initiative to donate the amount because you are Islamically required not to break your oath. Allah Says (what means): {But keep your oaths.} [Quran 5:89] Al-Baghawi said in his Tafseer: "It was said: This means, not to break the oath. It was also said, which is the most correct opinion that if one swears an oath, then he should not break it; so what is meant by it is to preserve the oath by not breaking it. This is if the oath is not related to abandoning what is recommended or doing what is disliked….." [End of quote]
The jurists stated that if a person swears an oath to do what is recommended, then it is desirable for him to fulfill his oath and it is disliked for him to break it. Ash-Sharbini, from the Shaafi'i School of jurisprudence stated in his book Mughni Al-Muhtaaj: "Whoever swears an oath to do what is recommended or abandon what is disliked, then it is disliked for him to break his oath…." [End of quote]
Besides, Sharh Al-Muntaha, which is a book from the Hanbali School of jurisprudence, reads: "Whoever swears an oath to do what is recommended or abandon what is disliked, then it is disliked for him to break his oath and it is desirable for him to fulfill it.…." [End of quote] Therefore, it is desirable for you, dear questioner, to take the initiative to donate the amount. If you did not donate it, you have done what is disliked and you must pay a ransom for breaking your oath.
2- You had intended a vow: meaning, you had intended that if you do that sin again, then you take a vow to donate that amount. Then this is considered a Lijaaj vow (a vow made in order to prevent oneself from something) because you had intended to prevent yourself from committing that sin. Ibn Qudaamah 
said about whoever breaks a Lijaaj vow: "He has the choice to either do what he has vowed to do, or to expiate for breaking his vow (oath)….” [End of quote]
The Fatwa of Sharaf Ad-Deen Al-Khaleeli ‘ala Al-Madh-hab Ash-Shaafi’i reads: "If a man made a vow that if he does a certain sin, then he would fast for ten years. However, he does the sin again, and he is unable to fulfill his vow, is it sufficient for him to expiate for breaking an oath instead of expiating for breaking a vow? He replied: ‘What this man did is Lijaaj vow (i.e. he vowed to prevent himself from doing a sin), and he has the choice between what he has committed himself to do, which is to fast, or to expiate for breaking an oath.' Al-‘Ibaab reads: 'If he had vowed (to do something) if he does the sin, then this is only Lijaaj, like if he is asked to drink wine, and then says: If I drink it, I have to do such and such…….'" [End of quote]
Allah knows best.