✅Answer: Please pay attention to the following narrations:

1 عَنِ الْحَلَبِيِّ عَنْ أَبِي عَبْداللَّهِ قَالَ: إِنَّهُ سُئِلَ عَنِ الْأَهِلَّةِ فَقَالَ هِيَ أَهِلَّةُ الشُّهُورِ فَإِذَا رَأَيْتَ الْهِلَالَ فَصُمْ وَ إِذَا رَأَيْتَهُ فَأَفْطِرْ.

📚 Al-Kafi, vol. 4, p. 76

Halabi said: Imam Sadiq (peace be upon him) was asked about the crescents; he said: They are the crescents of the months, so when you see the crescent, fast, and when you see it (at the end of Ramadan), break your fast!

2 عَنِ الصَّلْتِ الْخَزَّازِ عَنْ أَبِی عَبْداللَّه قَالَ: إِذَا غَابَ الْهِلَالُ قَبْلَ الشَّفَقِ فَهُوَ لِلَیْلَتِهِ وَ إِذَا غَابَ بَعْدَ الشَّفَقِ فَهُوَ لِلَیْلَتَیْنِ.

📚 Al-Kafi, vol. 4, p. 77

Imam Sadiq (peace be upon him) said: When the crescent disappears before twilight, it is for one night, and when it disappears after twilight, it is for two nights!

3 عَنْ أَبِي عَلِيِّ بْنِ رَاشِدٍ قَالَ: كَتَبَ إِلَيَّ أَبُو الْحَسَنِ الْعَسْكَرِيُّ كِتَاباً وَ أَرَّخَهُ يَوْمَ الثَّلَاثَاءِ لِلَيْلَةٍ بَقِيَتْ مِنْ شَعْبَانَ وَ ذَلِكَ فِي سَنَةِ اثْنَتَيْنِ وَ ثَلَاثِينَ وَ مِائَتَيْنِ وَ كَانَ يَوْمُ الْأَرْبِعَاءِ يَوْمَ شَكٍّ وَ صَامَ أَهْلُ بَغْدَادَ يَوْمَ الْخَمِيسِ وَ أَخْبَرُونِي أَنَّهُمْ رَأَوُا الْهِلَالَ لَيْلَةَ الْخَمِيسِ وَ لَمْ يَغِبْ إِلَّا بَعْدَ الشَّفَقِ بِزَمَانٍ طَوِيلٍ قَالَ فَاعْتَقَدْتُ أَنَّ الصَّوْمَ يَوْمَ الْخَمِيسُ وَ أَنَّ الشَّهْرَ كَانَ عِنْدَنَا بِبَغْدَادَ يَوْمَ الْأَرْبِعَاءِ قَالَ فَكَتَبَ إِلَيَّ زَادَكَ اللَّهُ تَوْفِيقاً فَقَدْ صُمْتَ بِصِيَامِنَا قَالَ ثُمَّ لَقِيتُهُ بَعْدَ ذَلِكَ فَسَأَلْتُهُ عَمَّا كَتَبْتُ بِهِ إِلَيْهِ فَقَالَ لِي أَ وَ لَمْ أَكْتُبْ إِلَيْكَ إِنَّمَا صُمْتُ الْخَمِيسَ وَ لَا تَصُمْ إِلَّا لِلرُّؤْيَةِ

📚 Al-Tahdhib, vol. 4, p. 167

Ali ibn Rashid said: The Imam (Abu al-Hasan al-Hadi, peace be upon him) wrote a letter to me and dated it on Tuesday, with one night remaining from Sha'ban, and this was in the year 232. And Wednesday was the day of doubt, and the people of Baghdad fasted on Thursday (as the month of Ramadan), and they informed me that they saw the crescent on Wednesday night and it did not disappear until a long time after the twilight had gone!

The narrator said: So I (based on the date of the Imam's letter which considered Wednesday the end of Sha'ban) believed that the fast (i.e., the first of Ramadan) was on Thursday, while for the people of Baghdad (based on the crescent disappearing a long time after twilight), the month of Ramadan was on Wednesday!

Then the Imam wrote to me: May Allah increase your success! You also fasted with our fast (meaning on Thursday)

Then after that, I met the Imam and asked him about the letter I had written to him; the Imam said: Did I not write to you that I fasted on Thursday! And do not fast except with the sighting of the crescent!

4 قَالَ أَبُو عَبْداللَّه: قَدْ يَكُونُ الْهِلَالُ لِلَيْلَةٍ وَ ثُلُثٍ وَ لَيْلَةٍ وَ نِصْفٍ وَ لَيْلَةٍ وَ ثُلُثَيْنِ وَ لِلَيْلَتَيْنِ إِلَّا شَيْئاً وَ هُوَ لِلَيْلَةٍ

📚 Al-Hidayah, p. 45

Imam Sadiq (peace be upon him) said: Sometimes the crescent is for one night and a third of a night! And sometimes for one and a half nights, and sometimes for one and two-thirds of a night, and sometimes for two nights, but a little less, and all of these are for one night!

✅ In dozens of valid and practiced Shia narrations, such as hadith 1 , the criterion for the beginning of Ramadan is the sighting of the crescent or the passing of 30 days from the month of Sha'ban.

In the single hadith 2 , it is stated that if the crescent disappears before twilight, i.e., before the redness on the western side is gone, it is for one night, and if it disappears after twilight, it is for two nights.

But in narration 3 , we see that despite the crescent disappearing after twilight on Wednesday night, the Imam still considered Thursday as the first day of the month!

And also in narration 2 , the setting of the crescent before twilight is only considered a sign of being the first night, but given narration 4 , there is no mention of the crescent for one and a third nights, one and a half nights, one and two-thirds of a night, and two nights but a little less, all of which have the ruling of being the first night, and it is obvious that the setting of these crescents occurs later, and therefore, the disappearance of the crescent after twilight is not always a sign of being the second night. And based on dozens of narrations about the criterion being the sighting, with the sky being clear on the sunset of the 29th of Sha'ban, the criterion is the sighting of the crescent, and if on the night after that, the crescent disappears a few moments after twilight, one cannot rule that the crescent is for two nights, and one should note that in the narrations, adding a day to the month of Ramadan without the sighting of the crescent or the passing of 30 days from the month of Sha'ban has been severely condemned.