✅Answer: Please pay attention to the following narrations:

1 مُعَاوِيَةَ بْنِ عَمَّارٍ عَنْ أَبِي عَبْداللَّه قَالَ: تُكَبِّرُ لَيْلَةَ الْفِطْرِ وَ صَبِيحَةَ الْفِطْرِ كَمَا تُكَبِّرُ فِي الْعَشْرِ

📚 Al-Kafi, vol. 4, p. 167

Imam Sadiq, peace and blessings of Allah be upon him, said: 'On the night of Eid al-Fitr and on the morning of Eid al-Fitr, you say the takbir, just as you say the takbir on the tenth (of the Eid al-Adha prayer)!'

2 عَنْ سَعِيدٍ النَّقَّاشِ قَالَ: قَالَ أَبُو عَبْداللَّه لِي أَمَا إِنَّ فِي الْفِطْرِ تَكْبِيراً وَ لَكِنَّهُ مَسْتور قَالَ قُلْتُ: وَ أَيْنَ هُوَ قَالَ فِي لَيْلَةِ الْفِطْرِ- فِي الْمَغْرِبِ وَ الْعِشَاءِ الْآخِرَةِ وَ فِي صَلَاةِ الْفَجْرِ وَ فِي صَلَاةِ الْعِيدِ ثُمَّ يَقْطَعُ قَالَ قُلْتُ: كَيْفَ أَقُولُ: قَالَ تَقُولُ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لَا إِلَهَ إِلَّا اللَّهُ وَ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ وَ لِلَّهِ الْحَمْدُ اللَّهُ أَكْبَرُ عَلَى مَا هَدَانَا- وَ هُوَ

قَوْلُ اللَّهِ عَزَّ وَ جَلَّ وَ لِتُكْمِلُوا الْعِدَّةَ يَعْنِي الصِّيَامَ وَ لِتُكَبِّرُوا اللَّهَ عَلى ما هَداكُمْ

📚 Al-Kafi, vol. 4, p. 166

Sa'id al-Naqqash said: 'Imam Sadiq, peace and blessings of Allah be upon him, said to me: 'Know that there is a takbir in Eid al-Fitr, but it is concealed!'

He said: 'I said: 'Where is it?' He said: 'On the night of Eid al-Fitr, after the Maghrib prayer and after the Isha prayer, and after the Fajr prayer, and after the Eid prayer, then he stops!'

He said: 'I said: 'How do I say it?' He said: 'You say:'

اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لَا إِلَهَ إِلَّا اللَّهُ وَ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ وَ لِلَّهِ الْحَمْدُ اللَّهُ أَكْبَرُ عَلَى مَا هَدَانَا

And this is the saying of Allah, the Almighty and Exalted (in chapter Al-Baqarah, verse 185) where He says: 'And so that you may complete the number' - meaning the number of fasting days - 'and that you may glorify Allah for what He has guided you to!'

3 الْفضل بْنِ شَاذَانَ عَنِ الرِّضَا أَنَّهُ كَتَبَ إِلَى الْمَأْمُونِ وَ التَّكْبِيرُ فِي الْعِيدَيْنِ وَاجِبٌ فِي الْفِطْرِ فِي دُبُرِ خَمْسِ صَلَوَاتٍ وَ يُبْدَأُ بِهِ فِي دُبُرِ صَلَاةِ الْمَغْرِبِ لَيْلَةَ الْفِطْر

📚 Uyun Akhbar al-Reza, vol. 2, p. 125

Imam Reza, peace and blessings of Allah be upon him, wrote to Ma'mun: 'And the takbir is obligatory in Eid al-Fitr and Eid al-Adha. In Eid al-Fitr, it is after five prayers, starting from the Maghrib prayer on the night of Eid al-Fitr....'

4️⃣ Al-A'mash narrated from Ja'far ibn Muhammad in the hadith of Shara'i al-Din, he said: 'And the takbir is obligatory in the two Eids. As for Eid al-Fitr, it is in five prayers, starting from the Maghrib prayer on the night of Eid al-Fitr until the Asr prayer on the day of Eid al-Fitr, and it is to say: 'Allahu Akbar, Allahu Akbar, la ilaha illa Allah, wa Allahu Akbar, wa li Allahi al-hamd, Allahu Akbar 'ala ma hadana, wa al-hamdu li Allahi 'ala ma ablana' (Allah is the greatest, Allah is the greatest, there is no god but Allah, and Allah is the greatest, and to Allah belongs all praise, Allah is the greatest for what He has guided us to, and praise be to Allah for what He has given us).'

📚 Al-Khisal, p. 609

In the hadith of Shara'i al-Din, Imam Sadiq, peace and blessings of Allah be upon him, said: 'And the takbir in Eid al-Fitr and Eid al-Adha is obligatory. As for Eid al-Fitr, it is in five prayers, starting from the Maghrib prayer on the night of Eid al-Fitr until the Asr prayer on the day of Eid al-Fitr, and it is to say:

اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لَا إِلَهَ إِلَّا اللَّهُ وَ اللَّهُ أَكْبَرُ وَ لِلَّهِ الْحَمْدُ اللَّهُ أَكْبَرُ عَلَى مَا هَدَانَا وَ الْحَمْدُ لِلَّهِ عَلَى مَا أَبْلَانَا

Because of the saying of Allah, the Almighty and Exalted (in chapter Al-Baqarah, verse 185) where He says:

لِتُكْمِلُوا الْعِدَّةَ وَ لِتُكَبِّرُوا اللَّهَ عَلى ما هَداكُمْ

Meaning: 'And so that you may complete the number (of fasting days) and that you may glorify Allah for what He has guided you to!'

✅ Based on the above narrations, when the crescent of the month of Shawwal is confirmed, after five prayers, meaning after the Maghrib prayer and after the Isha prayer on the night of Eid al-Fitr, and after the Fajr prayer and after the Dhuhr prayer and after the Asr prayer on the day of Eid al-Fitr, or after four prayers, meaning: after the Maghrib prayer and after the Isha prayer on the night of Eid al-Fitr, and after the Fajr prayer on the day of Eid al-Fitr, and after the Eid prayer, we say:

اللَّهُ أَکْبَرُ اللَّهُ أَکْبَرُ لَا إِلَهَ إِلَّا اللَّهُ وَ اللَّهُ أَکْبَرُ اللَّهُ أَکْبَرُ وَ لِلَّهِ الْحَمْدُ اللَّهُ أَکْبَرُ عَلَی مَا هَدَانَا

Or we say:

اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لَا إِلَهَ إِلَّا اللَّهُ وَ اللَّهُ أَكْبَرُ وَ لِلَّهِ الْحَمْدُ اللَّهُ أَكْبَرُ عَلَى مَا هَدَانَا وَ الْحَمْدُ لِلَّهِ عَلَى مَا أَبْلَانَا

✅ Of course, to act on both narrations, one can say these takbirat after the Maghrib prayer, the Isha prayer, the Fajr prayer, the Eid prayer, the Dhuhr prayer, and the Asr prayer.

✅ The takbirat of Eid al-Adha have some differences, which will be provided in separate narrations.

اللَّهُمَّ صَلِّ عَلَی مُحَمَّدٍ و آلِ مُحَمَّدٍ و عَجِّلْ لِوَلِیِّکَ الْفَرَج