✅Answer: Please pay attention to the following narrations:

1 عَمَّارِ بْنِ مُوسَى السَّابَاطِيِّ قَالَ: سَأَلْتُ أَبَا عَبْدِ اللَّهِ عَنْ شَيْ ءٍ مِنَ السَّهْوِ فِي الصَّلَاةِ فَقَالَ أَ لَا أُعَلِّمُكَ شَيْئاً إِذَا فَعَلْتَهُ ثُمَّ ذَكَرْتَ أَنَّكَ أَتْمَمْتَ أَوْ نَقَصْتَ لَمْ يَكُنْ عَلَيْكَ شَيْ ءٌ قُلْتُ بَلَى قَالَ إِذَا سَهَوْتَ فَابْنِ عَلَى الْأَكْثَرِ فَإِذَا فَرَغْتَ وَ سَلَّمْتَ فَقُمْ فَصَلِّ مَا ظَنَنْتَ أَنَّكَ نَقَصْتَ فَإِنْ كُنْتَ قَدْ أَتْمَمْتَ لَمْ يَكُنْ عَلَيْكَ فِي هَذِهِ شَيْ ءٌ وَ إِنْ ذَكَرْتَ أَنَّكَ كُنْتَ نَقَصْتَ كَانَ مَا صَلَّيْتَ تَمَامَ مَا نَقَصْتَ

📚 Tahdhib, Vol. 2, p. 349

Ammar said: I asked Imam Sadiq (peace be upon him) about something concerning inadvertence in prayer; the Imam said: 'Shall I not teach you something that if you do it and then remember that you have completed it or shorted it, there will be nothing on you?' I said: 'Yes!'

He said: 'When you are in a state of inadvertence, build upon the greater number, and when you are finished and have given the salutation, stand up and perform what you think you have shorted! So, if you have completed the prayer, there is nothing on you in this (precautionary prayer), and if you remember that you have shorted the prayer, what you have performed will be a completion of what you have shorted!'

2 عُبَيْدِ بْنِ زُرَارَة عن أَبِي عَبْداللَّه قَالَ: سَأَلْتُهُ عَنْ رَجُلٍ لَمْ يَدْرِ رَكْعَتَيْنِ صَلَّى أَمْ ثَلَاثاً قَالَ يُعِيدُ قُلْتُ أَ لَيْسَ يُقَالُ لَا يُعِيدُ الصَّلَاةَ فَقِيهٌ فَقَالَ إِنَّمَا ذَلِكَ فِي الثَّلَاثِ وَ الْأَرْبَعِ

📚 Tahdhib, Vol. 2, p. 193

Ubayd ibn Zurarah said: I asked Imam Sadiq (peace be upon him) about a person who does not know if he has performed two rak'ahs or three rak'ahs; the Imam said: 'He should repeat the prayer!'

I said: 'Is it not said that a jurisprudent does not repeat his prayer?!'

The Imam said: 'This is regarding the third and fourth rak'ahs!'

3 زُرَارَةَ عَنْ أَحَدِهِمَا قَالَ: قُلْتُ لَهُ رَجُلٌ لَمْ يَدْرِ اثْنَتَيْنِ صَلَّى أَمْ ثَلَاثاً فَقَالَ إِنْ دَخَلَهُ الشَّكُّ بَعْدَ دُخُولِهِ فِي الثَّالِثَةِ مَضَى فِي الثَّالِثَةِ ثُمَّ صَلَّى الْأُخْرَى وَ لَا شَيْ ءَ عَلَيْهِ وَ يُسَلِّمُ

📚 Al-Kafi, Vol. 3, p. 350

Zurarah said: I said to Imam Baqir or Imam Sadiq (peace be upon them both): 'A person does not know whether he has performed two rak'ahs or three rak'ahs! (What should he do)?'

The Imam said: 'If the doubt comes to him after he has entered the third rak'ah (i.e., the rak'ah that is at least the third and the doubt occurred in its range), he should proceed with the third (i.e., he should build upon the previous rak'ah having been the third and continue the prayer until its end) and then (after the prayer) perform another rak'ah (known as the precautionary prayer) and there is nothing on him and he should give the salutation!'

4 عَنِ الْعَلَاءِ قال: قُلْتُ لِأَبِي عَبْداللَّه رَجُلٌ صَلَّى رَكْعَتَيْنِ وَ شَكَّ فِي الثَّالِثَةِ قَالَ يَبْنِي عَلَى الْيَقِينِ فَإِذَا فَرَغَ تَشَهَّدَ وَ قَامَ قَائِماً فَصَلَّى [یصلی] رَكْعَةً بِفَاتِحَةِ الْقُرْآنِ

📚 Qurb al-Isnad, p. 16

Ala' said: I said to Imam Sadiq (peace be upon him): 'A person performs two rak'ahs of prayer and doubts in the third. (What should he do?)'

He said: 'He should build upon certainty (i.e., upon something that he is certain will fulfill his duty, which is explained in hadiths 1 and 3), so when he is finished, he should recite the tashahhud (and give the salutation) and stand up and perform one rak'ah of prayer with Surah al-Hamd (which is the prayer known as the precautionary prayer)!'

5 عَنْ إِسْحَاقَ بْنِ عَمَّارٍ قَالَ: سَأَلْتُ أَبَا الْحَسَنِ مُوسَى بْنَ جَعْفَرٍ كَيْفَ صَارَتِ الصَّلَاةُ رَكْعَةً وَ سَجْدَتَيْنِ وَ كَيْفَ إِذَا صَارَتْ سَجْدَتَيْنِ لَمْ تَكُنْ رَكْعَتَيْنِ......

وَ إِنَّمَا كَانَتِ الصَّلَاةُ الَّتِي أُمِرَ بِهَا رَكْعَتَيْنِ وَ سَجْدَتَيْنِ وَ هُوَ إِنَّمَا سَجَدَ سَجْدَتَيْنِ فِي كُلِّ رَكْعَةٍ كَمَا أَخْبَرْتُكَ مِنْ تَذَكُّرِهِ لِعَظَمَةِ رَبِّهِ تَبَارَكَ وَ تَعَالَى فَجَعَلَهُ اللَّهُ عَزَّ وَ جَلَّ فَرْضاً الْحَدِيثَ.

📚 Ilal al-Shara'i, p. 334

Ishaq ibn Ammar said: I asked Imam Kazim (peace be upon him): 'Why does the prayer have one bowing and two prostrations and how is it that (each rak'ah) has two prostrations but not two bowings?'

The Imam, after narrating the first prayer of the Messenger of Allah (peace and blessings be upon him and his family) in the heavens, said: 'Indeed, the prayer that has been commanded is two rak'ahs with two prostrations, and its explanation is that two prostrations are performed in each rak'ah....'

✅ Continuation of the previous post, regarding the ruling of doubt between two and three rak'ahs in a four-rak'ah prayer:

6 عَنْ عَنْبَسَةَ بْنِ مُصْعَبٍ قَالَ: قَالَ لِي أَبُو عَبْدِ اللَّه إِذَا شَكَكْتَ فِي الرَّكْعَتَيْنِ الْأَوَّلَتَيْنِ فَأَعِدْ.

📚 Al-Tahdhib, Vol. 2, p. 176

Anbasah said: Imam Sadiq (peace be upon him) said to me: 'When you doubt in the first two rak'ahs of the prayer, repeat the prayer!'

7 عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ حَفْصِ بْنِ الْبَخْتَرِيِّ وَ غَيْرِ وَاحِدٍ كُلِّهِمْ عَنْ أَبِي عَبْدِ اللَّه قَالَ: إِذَا شَكَكْتَ فِي الْمَغْرِبِ فَأَعِدْ وَ إِذَا شَكَكْتَ فِي الْفَجْرِ فَأَعِدْ.

📚 Al-Tahdhib, Vol. 2, p. 180

Imam Sadiq (peace be upon him) said: 'When you doubt in the Maghrib prayer, repeat the prayer, and when you doubt in the Fajr prayer, also repeat the prayer!'

✅ Doubt between two and three rak'ahs in a four-rak'ah prayer has two states:

1. The doubt enters a person before entering the third rak'ah, i.e., the rak'ah that is at least the third, in a way that we doubt: Is this rak'ah we have now stood up for or are busy reciting the second or the third rak'ah? Since such a doubt has occurred in the first two rak'ahs (i.e., the second rak'ah of the first two rak'ahs of the prayer), according to numerous narrations like narration 6, it invalidates the prayer and the prayer must be repeated.

2. The second state is that the doubt enters us after entering the third rak'ah, i.e., the rak'ah that is at least the third, in a way that we doubt whether this rak'ah that we have just finished was the second or the third!

This doubt has entered us in the range of at least the third rak'ah and is not a case of invalidating the prayer. Its ruling is mentioned in narrations 3, 4, and the general narration 1, and others.

According to the mentioned narrations, the person should build upon the greater number, which is three rak'ahs, and in reality, he builds upon the fact that this rak'ah that he has just finished was the third, and therefore this rak'ah he is currently in is the fourth. With this calculation, he completes his prayer, and after the prayer, he stands up and performs a one-rak'ah prayer with Surah al-Hamd, which is known as the precautionary prayer!

✅ Two points:

Point 1: According to Shi'a narrations, like narration 5, the end of each rak'ah of prayer is the completion of the two prostrations. Therefore, if the doubt enters after the two prostrations have been completed, it is subject to the rulings of inadvertence, and if the doubt occurs before the two prostrations are completed, it is subject to the first state, i.e., invalidation and repetition of the prayer, because we have in fact doubted whether this rak'ah I am now performing is the second or the third, and such a doubt is considered doubting in the first two rak'ahs of the prayer.

✅ Point 2: According to numerous narrations, the rulings of doubts are related to four-rak'ah prayers, and doubt in the Maghrib prayer and the Fajr prayer leads to invalidation and the necessity of repetition, which is mentioned in narration 7, among others. Therefore, the rulings for doubting between two and three rak'ahs are related to the four-rak'ah prayer.

✅ It is also essential to refer to the following post, in two parts, for the method of the precautionary prayer:

https://feghh14.com/en/922