✅Answer: Please pay attention to the following narrations:

1 عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ زِيَادِ بْنِ أَبِي الْحَلَّالِ قَالَ: قَالَ لَنَا أَبُو عَبْدِ اللَّهِ لَا صِيَامَ بَعْدَ الْأَضْحَى ثَلَاثَةَ أَيَّامٍ وَ لَا بَعْدَ الْفِطْرِ ثَلَاثَةَ أَيَّامٍ إِنَّهَا أَيَّامُ أَكْلٍ وَ شُرْبٍ.

📚 Al-Tahdhib Vol. 4, p. 330

📚 Al-Kafi Vol. 4, p. 148

Ziyad ibn Abi Halal said: Imam Sadiq (peace be upon him) said to us: 'There is no fasting for three days after Eid al-Adha and three days after Eid al-Fitr, because these are days of eating and drinking!'

2 عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْحَجَّاجِ قَالَ: سَأَلْتُ أَبَا الحسن عَنِ الْيَوْمَيْنِ اللَّذَيْنِ بَعْدَ الْفِطْرِ- أَ يُصَامَانِ أَمْ لَا فَقَالَ أَكْرَهُ لَكَ أَنْ تَصُومَهُمَا.

2 Al-Kafi Vol. 4, p. 148

Abdul-Rahman ibn Hajjaj said: 'I asked Imam Kadhim (peace be upon him) about the two days after Eid al-Fitr, whether they could be fasted or not? He said: 'I advise you against fasting these two days!'

3 عَنْ مُحَمَّدِ بْنِ إِسْمَاعِيلَ عَنْ حَمَّادِ بْنِ عِيسَى عَنْ حَرِيزٍ عَنْهُمْ قَالَ: إِذَا أَفْطَرْتَ مِنْ رَمَضَانَ فَلَا تَصُومَنَّ [من] بَعْدَ الْفِطْرِ تَطَوُّعاً إِلَّا بَعْدَ ثَلَاثٍ يَمْضِينَ.

📚 Al-Tahdhib Vol. 4, p. 298

Hariz narrated from the Ahl al-Bayt (peace be upon them) that they said: 'When you break the fast of the month of Ramadan (at its end), do not fast a voluntary (recommended) fast after the day of Eid al-Fitr unless three days (of the month of Shawwal) have passed!'

✅As is clear from the above narrations, the Ahl al-Bayt (peace be upon them) have prohibited fasting for two or three days after Eid al-Fitr as a reprehensible act and have designated them as days of eating and drinking.

✅Unfortunately, some who claim to practice Islamic medicine consider fasting one day after Eid al-Fitr to be good and, in addition to praising fasting after the day of Eid al-Fitr from a medical perspective, they also attribute its being a tradition to Shi'a jurisprudence, whereas the falsity of this claim is clear from the above narrations. Although fasting one day after Eid al-Fitr is not forbidden, and in the narration of Zuhri from Imam Sajjad (peace be upon him) in 📚 Al-Faqih Vol. 2, p. 77, it is stated that a person has the choice to fast on the first six days of the month of Shawwal (except for the day of Eid al-Fitr, on which fasting is forbidden) and can fast them if they wish, but in the above narrations, it has been mentioned as a reprehensible act and is prohibited.

Reprehensibility of fasting three days after Eid al-Fitr

اللَّهُمَّ صَلّ عَلَی مُحَمَّدٍ وَ آلِ مُحَمَّدٍ

وَ عَجِّلْ لِوَلِیِّکَ الْفَرَجَ وَ الْعَافِیَةَ وَ النَّصْرَ