✅ Answer: Refer to the following narrations:

Doubts in Prayer

1⃣عَنْ أَبِي عَبْداللَّه أَنَّهُ قَالَ لَهُ يَا عَمَّارُ أَجْمَعُ لَكَ السَّهْوَ كُلَّهُ فِي كَلِمَتَيْنِ مَتَى مَا شَكَكْتَ فَخُذْ بِالْأَكْثَرِ فَإِذَا سَلَّمْتَ فَأَتِمَّ مَا ظَنَنْتَ أَنَّكَ نَقَصْتَ

📚 Al-Faqih, Vol. 1, p. 340

Imam Sadiq (peace be upon him) said: O Ammar! I will summarize all the rules of forgetfulness for you in two words! Whenever you doubt, take the majority (assume the higher number) and when you say the tasleem, complete what you think you have missed (with the prayer known as the precautionary prayer).

2⃣عَنِ ابْنِ أَبِی یَعْفُورٍ قَالَ: سَأَلْتُ أَبَا عَبْداللَّه عَنِ الرَّجُلِ لَا یَدْرِی رَکْعَتَیْنِ صَلَّی أَمْ أَرْبَعاً قَالَ یَتَشَهَّدُ و یُسَلِّمُ ثُمَّ یَقُومُ فَیُصَلِّی رَکْعَتَیْنِ وَ أَرْبَعَ سَجَدَاتٍ یَقْرَأُ فِیهِمَا بِفَاتِحَةِ الْکِتَابِ ثُمَّ یَتَشَهَّدُ وَ یُسَلِّمُ وَ إِنْ کَانَ صَلَّی أَرْبَعاً کَانَتْ هَاتَانِ نَافِلَةً وَ إِنْ کَانَ صَلَّی رَکْعَتَیْنِ کَانَتْ هَاتَانِ تَمَامَ الْأَرْبَعِ وَ إِنْ تَکَلَّمَ فَلْیَسْجُدْ سَجْدَتَیِ السَّهْو

📚 Al-Kafi, Vol. 3, p. 352

Ibn Abi Ya'fur said: I asked Imam Sadiq (peace be upon him) about someone who doesn't know whether they have prayed two rak'ahs or four rak'ahs; he said: They should recite the tashahhud and say the tasleem, then stand up and pray two rak'ahs with four prostrations, reciting only Surah Al-Hamd, then recite the tashahhud and say the tasleem.

If they had prayed four rak'ahs, these two rak'ahs are considered nafl (supererogatory) prayers, and if they had prayed two rak'ahs, these two rak'ahs complete the four. And if they spoke (after the tasleem and before the precautionary prayer), they should perform two prostrations of forgetfulness.

3⃣عن الْحَلَبِيِّ عَنْ أَبِي عَبْداللَّه أَنَّهُ قَالَ: إِذَا لَمْ تَدْرِ اثْنَتَيْنِ صَلَّيْتَ أَمْ أَرْبَعاً وَ لَمْ يَذْهَبْ وَهْمُكَ إِلَى شَيْءٍ فَتَشَهَّدْ وَ سَلِّمْ ثُمَّ صَلِّ رَكْعَتَيْنِ وَ أَرْبَعَ سَجَدَاتٍ تَقْرَأُ فِيهِمَا بِأُمِّ الْكِتَابِ ثُمَّ تَشَهَّدُ وَ تُسَلِّمُ فَإِنْ كُنْتَ إِنَّمَا صَلَّيْتَ رَكْعَتَيْنِ كَانَتَا هَاتَانِ تَمَامَ الْأَرْبَعِ و إِنْ كُنْتَ صَلَّيْتَ أَرْبَعاً كَانَتَا هَاتَانِ نَافِلَةً

📚 Al-Faqih, Vol. 1, p. 349

Imam Sadiq (peace be upon him) said: If you do not know whether you have prayed two rak'ahs or four rak'ahs and your mind is not inclined to either side, then recite the tashahhud and say the tasleem, then pray two rak'ahs with four prostrations, reciting Surah Al-Hamd, then recite the tashahhud and say the tasleem. If you had prayed two rak'ahs, these two rak'ahs complete it, and if you had prayed four rak'ahs, these two rak'ahs are nafl.

4⃣عن زرارة عن أحدهما قال: قُلْتُ لَهُ مَنْ لَمْ یَدْرِ فِی أَرْبَعٍ هُوَ أَمْ فِی ثِنْتَیْنِ وَ قَدْ أَحْرَزَ الثِّنْتَیْنِ قَالَ یَرْکَعُ رَکْعَتَیْنِ وَ أَرْبَعَ سَجَدَاتٍ وَ هُوَ قَائِمٌ بِفَاتِحَةِ الْکِتَابِ وَ یَتَشَهَّدُ وَ لَا شَیْءَ عَلَیْهِ...

📚 Al-Kafi, Vol. 3, p. 351

Imam Sadiq or Imam Baqir (peace be upon them) said regarding someone who does not know if they are in the second or fourth rak'ah, but is sure of two rak'ahs: (They should assume it is the fourth and after the prayer) pray two rak'ahs with four prostrations, reciting Surah Al-Hamd, and recite the tashahhud, and nothing is upon them.

5⃣عن جَمِیلٍ عَنْ بَعْضِ أَصْحَابِنَا عَنْ أَبِی عَبْدِ اللَّهِ فِی حَدِیثٍ قَالَ: فِی رَجُلٍ لَمْ یَدْرِ اثْنَتَیْنِ صَلَّی أَمْ أَرْبَعاً وَ وَهْمُهُ یَذْهَبُ إِلَی الْأَرْبَعِ أَوْ إِلَی الرَّکْعَتَیْنِ فَقَالَ یُصَلِّی رَکْعَتَیْنِ وَ أَرْبَعَ سَجَدَاتٍ وَ قَالَ إِنْ ذَهَبَ وَهْمُکَ إِلَی رَکْعَتَیْنِ وَ أَرْبَعٍ فَهُوَ سَوَاءٌ وَ لَیْسَ الْوَهْمُ فِی هَذَا الْمَوْضِعِ مِثْلَهُ فِی الثَّلَاثِ وَ الْأَرْبَعِ.

📚 Al-Kafi, Vol. 3, p. 353

Imam Sadiq (peace be upon him) said about someone who does not know if they have prayed two rak'ahs or four rak'ahs, and their mind leans towards four or two rak'ahs: They should pray two rak'ahs (of precautionary prayer) with four prostrations!

And he said: If your mind leans equally towards two rak'ahs and four rak'ahs, it is the same, and the doubt here is not like the doubt between three and four.

✅ According to the above and other narrations, if someone in a four-rak'ah prayer doubts whether they have prayed two or four rak'ahs and is certain of completing at least two rak'ahs, they should assume they have prayed four rak'ahs and after the tasleem, perform two rak'ahs of the precautionary prayer.

Performing prostrations of forgetfulness is also necessary if they spoke after the tasleem and before performing the precautionary prayer.

اللَّهُمَّ فَصَلِّ عَلَی مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ عَجِّلْ لِوَلِیِّکَ الْفَرَجَ وَ الْعَافِیَةَ وَ النَّصْرَ