✅Answer: Please pay attention to the following narrations:

عَنْ أَبِي جَعْفَرٍ قَالَ: مَنْ صَامَ شَعْبَانَ كَانَ لَهُ طَهُوراً مِنْ كُلِّ زَلَّةٍ وَ وَصْمَةٍ وَ بَادِرَةٍ قَالَ أَبُو حَمْزَةَ لِأَبِي جَعْفَرٍ مَا الْوَصْمَةُ قَالَ الْيَمِينُ فِي الْمَعْصِيَةِ وَ النَّذْرُ فِي مَعْصِيَةٍ قُلْتُ فَمَا الْبَادِرَةُ قَالَ الْيَمِينُ عِنْدَ الْغَضَبِ وَ التَّوْبَةُ مِنْهَا النَّدَمُ عَلَيْهَا

📚Al-Faqih, Vol. 2, p. 92

Translation: Imam Baqir (peace be upon him) said: 'Whoever fasts the month of Sha'ban, for him there will be purification from every slip, 'wasmah,' and 'badirah.' Abu Hamza said: 'I said to Imam Baqir (peace be upon him): 'What is 'wasmah'?' He said: 'Swearing an oath in disobedience and vowing in disobedience.' I said: 'What is 'badirah'?' He said: 'It is swearing an oath in a state of anger, and repentance from it is regret and remorse for it.'

عَنْ عَبْدِ اللَّهِ بْنِ سِنَانٍ عَنْ أَبِي عَبْدِ اللَّهِ قَالَ: قَالَ: لَا يَمِينَ فِي غَضَبٍ وَ لَا فِي قَطِيعَةِ رَحِمٍ الْحَدِيثَ.

📚Al-Kafi, Vol. 7, p. 442

Translation: Imam Sadiq (peace be upon him) said: 'There is no oath or swearing in a state of anger and regarding severing ties with kin.'

'Meaning such an oath is not valid.'

✅It is clear from the above narration and other narrations that if a person swears an oath in a state of anger, such an oath is not valid and has no weight. Of course, according to the first narration, it is a type of disobedience, and to be purified from it, one can fast in the month of Sha'ban, and repentance from it is remorse and regret for it.

Therefore, the oath in question, which was made in a state of anger, has no weight, and one should only be remorseful for it.

✅Even if this oath was not made in a state of anger, pay attention to the following narrations as well:

عَنْ سَعِيدٍ الْأَعْرَجِ قَالَ: سَأَلْتُ أَبَا عَبْدِ اللَّهِ عَنِ الرَّجُلِ يَحْلِفُ عَلَى الْيَمِينِ فَيَرَى أَنَّ تَرْكَهَا أَفْضَلُ وَ إِنْ تَرَكَهَا خَشِيَ أَنْ يَأْثَمَ أَ يَتْرُكُهَا قَالَ أَ مَا سَمِعْتَ قَوْلَ رَسُولِ اللَّهِ ص- إِذَا رَأَيْتَ خَيْراً مِنْ يَمِينِكَ فَدَعْهَا

📚Al-Kafi, Vol. 7, p. 444

Translation: Sa'id said: 'I asked Imam Sadiq (peace be upon him) about a person who makes an oath but sees that it is better to abandon that action, and if he abandons that action, he is afraid that he has sinned. Can he abandon it?' The Imam said: 'Have you not heard the saying of the Messenger of Allah (peace be upon him and his family) who said: 'When you see something better than your oath, abandon your oath.'

عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي عَبْدِ اللَّهِ عَنْ أَبِي عَبْدِ اللَّهِ قَالَ: إِذَا حَلَفَ الرَّجُلُ عَلَى شَيْ ءٍ وَ الَّذِي حَلَفَ عَلَيْهِ إِتْيَانُهُ خَيْرٌ مِنْ تَرْكِهِ فَلْيَأْتِ الَّذِي هُوَ خَيْرٌ وَ لَا كَفَّارَةَ عَلَيْهِ وَ إِنَّمَا ذَلِكَ مِنْ خُطُوَاتِ الشَّيْطَانِ

📚Al-Kafi, Vol. 7, p. 443

Translation: Imam Sadiq (peace be upon him) said: 'When a person swears an oath on something and doing what he swore on is better than abandoning it, then he should do what he swore on, and there is no atonement on him, for this is from the footsteps of Satan.'

عَنْ أَبِي عَبْدِ اللَّهِ قَالَ: مَنْ حَلَفَ عَلَى يَمِينٍ فَرَأَى غَيْرَهَا خَيْراً مِنْهَا فَأَتَى ذَلِكَ فَهُوَ كَفَّارَةُ يَمِينِهِ وَ لَهُ حَسَنَةٌ

📚Al-Kafi, Vol. 7, p. 443

Translation: Imam Sadiq (peace be upon him) said: 'Whoever swears an oath and sees that something else is better than it and does it, this will be the atonement for his oath, and it will also be a good deed for him.'

✅According to the above narrations, a person who, after swearing an oath, sees that doing something other than what he swore on is better, should abandon his oath and do the better thing, and this will be the atonement for his oath, and at the same time, he will be given a good deed. In the case mentioned in the question, now that the person sees that not selling the car is better for him, he should abandon his oath and refrain from selling the car, and there is no atonement on him.

Swearing an oath