✅Answer: Please pay attention to the following narrations:

1 حفص بن غياث عن أَبِي عبداللَّه قال: سَأَلْتُهُ عَنْ كَفَّارَةِ النَّذْرِ فَقَالَ كَفَّارَةُ النَّذْرِ كَفَّارَةُ الْيَمِين

📚Al-Kafi, Vol. 7, p. 457

Hafs said: 'I asked Imam Sadiq (peace be upon him) about the expiation for a vow.' He said: 'The expiation for a vow is the same as the expiation for an oath!'

2 عن أَبِي الْحَسَن مُوسَى أَنَّهُ قَالَ: كُلُّ مَنْ عَجَزَ عَنْ نَذْرٍ نَذَرَهُ فَكَفَّارَتُهُ كَفَّارَةُ يَمِينٍ

📚Al-Kafi, Vol. 7, p. 457

Imam Kadhim (peace be upon him) said: 'Whoever is unable to fulfill a vow he has made, its expiation is the expiation of an oath!'

3️⃣Imam Sadiq (peace be upon him) said about the expiation for an oath: 'He should feed ten needy people, for each needy person one 'mudd' and a handful of wheat or flour, or clothe those ten needy people, with two garments for each, or free a slave. And he has a choice between these three, to do whichever he wishes. And if he is unable to do any of these three, then he must fast for three days!'

📚Al-Kafi, Vol. 7, p. 451

4 علي بن أَبي حمزة عن أَبِي عَبْداللَّه قَالَ: سَأَلْتُهُ عَنْ كَفَّارَةِ الْيَمِينِ فَقَالَ عِتْقُ رَقَبَةٍ أَوْ كِسْوَةٌ وَ الْكِسْوَةُ ثَوْبَانِ أَوْ إِطْعَامُ عَشَرَةِ مَسَاكِينَ أَيَّ ذَلِكَ فَعَلَ أَجْزَأَ عَنْهُ فَإِنْ لَمْ يَجِدْ فَصِيَامُ ثَلَاثَةِ أَيَّامٍ مُتَوَالِيَاتٍ وَ إِطْعَامُ عَشَرَةِ مَسَاكِينَ مُدّاً مُدّاً

📚Al-Kafi, Vol. 7, p. 452

Ali ibn Abi Hamza said: 'I asked Imam Sadiq (peace be upon him) about the expiation for an oath.' The Imam said: 'Freeing a slave, or clothing (ten needy people), which is two garments, or feeding ten needy people, any of which he does is sufficient. And if he is unable, then he must fast for three consecutive days.'

And feeding ten needy people is one 'mudd' for each!

5 إِسْحَاقَ بْنِ عَمَّارٍ عَنْ أَبِي إِبْرَاهِيم قَالَ: سَأَلْتُهُ عَنْ كَفَّارَةِ الْيَمِينِ فِي قَوْلِهِ فَمَنْ لَمْ يَجِدْ فَصِيامُ ثَلاثَةِ أَيَّامٍ مَا حَدُّ مَنْ لَمْ يَجِدْ وَ إِنَّ الرَّجُلَ لَيَسْأَلُ فِي كَفِّهِ وَ هُوَ يَجِدُ فَقَالَ إِذَا لَمْ يَكُنْ عِنْدَهُ فَضْلٌ عَنْ قُوتِ عِيَالِهِ فَهُوَ مِمَّنْ لَا يَجِدُ

📚Al-Kafi, Vol. 7, p. 452

Ishaq ibn Ammar said: 'I asked Imam Kadhim (peace be upon him) about the expiation for an oath regarding the Almighty's saying (in Surah Al-Ma'idah, 89): 'But whoever cannot find (the means to feed ten needy people or clothe them or free a slave), then he must fast for three days.' 'What is the limit of not being able to find the means, for indeed a person begs with his hand outstretched while he has the means!'

The Imam said: 'When he does not have more than the sustenance of his family with him, he is among those who do not have the means!'

Allah Almighty says:

لَا يُؤَاخِذُكُمُ اللَّهُ بِاللَّغْوِ فِي أَيْمَانِكُمْ وَلَكِن يُؤَاخِذُكُم بِمَا عَقَّدتُّمُ الْأَيْمَانَ فَكَفَّارَتُهُ إِطْعَامُ عَشَرَةِ مَسَاكِينَ مِنْ أَوْسَطِ مَا تُطْعِمُونَ أَهْلِيكُمْ أَوْ كِسْوَتُهُمْ أَوْ تَحْرِيرُ رَقَبَةٍ فَمَن لَّمْ يَجِدْ فَصِيَامُ ثَلَاثَةِ أَيَّامٍ ذَلِكَ كَفَّارَةُ أَيْمَانِكُمْ إِذَا حَلَفْتُمْ وَاحْفَظُوا أَيْمَانَكُمْ

Allah will not hold you accountable for your unintentional oaths, but He will hold you accountable for your deliberate oaths. So its expiation is feeding ten poor people from the average of what you feed your families, or clothing them, or freeing a slave. But whoever cannot find (the means to do that), then he must fast for three days. This is the expiation for your oaths when you have sworn (and broken them), and you must guard your oaths (and not break them).

6 عَنْ أَبِي عبداللَّه فِي قَوْل اللَّهِ عَزَّ وَ جَلَّ مِنْ أَوْسَطِ ما تُطْعِمُونَ أَهْلِيكُمْ قَالَ هُوَ كَمَا يَكُونُ أَنَّهُ يَكُونَ فِي الْبَيْتِ مَنْ يَأْكُلُ أَكْثَرَ مِنَ الْمُدِّ وَ مِنْهُمْ مَنْ يَأْكُلُ أَقَلَّ مِنَ الْمُدِّ فَبَيْنَ ذَلِكَ وَ إِنْ شِئْتَ جَعَلْتَ لَهُمْ أُدْماً وَ الْأُدْمُ أَدْنَاهُ مِلْحٌ وَ أَوْسَطُهُ الْخَلُّ وَ الزَّيْتُ وَ أَرْفَعُهُ اللَّحْمُ

📚Al-Kafi, Vol. 7, p. 453

Imam Sadiq (peace be upon him) said regarding the Almighty's saying (in Surah Al-Ma'idah, verse 89): 'from the average of what you feed your families,' he said: 'It is as such in the houses of those who eat more than one 'mudd' and there are those who eat less than one 'mudd', so this (i.e., one 'mudd') is given. And if you wish, you can provide condiments for those needy people, and the least of the condiments is salt, the average is vinegar and olive oil, and the highest is meat!'

✅According to the above and other narrations, the expiation for a vow is the same as the expiation for an oath, which has been explained in the above narrations.