✅Answer: Pay attention to the following narrations:

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

📚 Al-Faqih, vol.1, p.340

Imam al-Sadiq (peace be upon him) said to ‘Ammar: O ‘Ammar! I will summarize all the rulings of forgetfulness for you in two words: whenever you doubt, take the higher number, and when you have given the salām, complete what you think you may have left incomplete.

2 عن بَعْض أَصْحَابِنَا عن أَبِي عَبْداللَّه قَالَ: فِيمَنْ لَا يَدْرِي أَ ثَلَاثاً صَلَّى أَمْ أَرْبَعاً وَ وَهْمُهُ فِي ذَلِكَ سَوَاءٌ قَالَ فَقَالَ إِذَا اعْتَدَلَ الْوَهْمُ فِي الثَّلَاثِ وَ الْأَرْبَعِ فَهُوَ بِالْخِيَارِ إِنْ شَاءَ صَلَّى رَكْعَةً وَ هُوَ قَائِمٌ وَ إِنْ شَاءَ صَلَّى رَكْعَتَيْنِ وَ أَرْبَعَ سَجَدَاتٍ و هُوَ جَالِسٌ

📚 Al-Kafi, vol.3, p.353

Imam al-Sadiq (peace be upon him), regarding a person who does not know whether he has prayed three rak‘ahs or four and his assumption about it is equal, said: When the doubt about three and four is equal, the person is given a choice: if he wishes, he may pray one rak‘ah (known as the precautionary prayer) standing, and if he wishes, he may pray two rak‘ahs with four prostrations sitting.

3 عن الْحَلَبِي عَنْ أَبِي عَبْداللَّهِ فِي حَدِيثٍ قَالَ: إِذَا كُنْتَ لَا تَدْرِي ثَلَاثاً صَلَّيْتَ أَمْ أَرْبَعاً وَ لَمْ يَذْهَبْ وَهْمُكَ إِلَى شَيْ ءٍ فَسَلِّمْ ثُمَّ صَلِّ رَكْعَتَيْنِ وَ أَنْتَ جَالِسٌ تَقْرَأُ فِيهِمَا بِأُمِّ الْكِتَابِ- وَ إِنْ ذَهَبَ وَهْمُكَ إِلَى الثَّلَاثِ فَقُمْ فَصَلِّ الرَّكْعَةَ الرَّابِعَةَ وَ لَا تَسْجُدْ سَجْدَتَيِ السَّهْوِ فَإِنْ ذَهَبَ وَهْمُكَ إِلَى الْأَرْبَعِ فَتَشَهَّدْ وَ سَلِّمْ ثُمَّ اسْجُدْ سَجْدَتَيِ السَّهْو

📚 Al-Kafi, vol.3, p.353

Imam al-Sadiq (peace be upon him) said: When you do not know whether you have prayed three rak‘ahs or four, and your opinion does not lean toward either, then give the salām and pray two rak‘ahs sitting, reciting only Sūrat al-Hamd in them. If your thought leans toward three rak‘ahs, then stand and pray the fourth rak‘ah, and do not perform two prostrations of forgetfulness. And if your thought leans toward four rak‘ahs, then recite tashahhud, give the salām, and perform two prostrations of forgetfulness.

4 الْحُسَيْنِ بْنِ أَبِي الْعَلَاءِ عَنْ أَبِي عَبْدِ اللَّه قَالَ: إِنِ اسْتَوَى وَهْمُهُ فِي الثَّلَاثِ وَ الْأَرْبَعِ سَلَّمَ وَ صَلَّى رَكْعَتَيْنِ وَ أَرْبَعَ سَجَدَاتٍ بِفَاتِحَةِ الْكِتَابِ وَ هُوَ جَالِسٌ يُقَصِّرُ [يقصد] فِي التَّشَهُّد

📚 Al-Kafi, vol.3, p.351

Imam al-Sadiq (peace be upon him) said: If his doubt between three and four is equal, he gives salām and prays two rak‘ahs sitting with only Sūrat al-Hamd and with four prostrations, shortening the tashahhud.

5 عَبْدالرَّحْمَنِ بْنِ سَیَابَةَ وَ أَبِی الْعَبَّاسِ عَنْ أَبِی عَبْداللَّه قَالَ: إِذَا لَمْ تَدْرِ ثَلَاثاً صَلَّیْتَ أَوْ أَرْبَعاً وَ وَقَعَ رَأْیُکَ عَلَی الثَّلَاثِ فَابْنِ عَلَی الثَّلَاثِ وَ إِنْ وَقَعَ رَأْیُکَ عَلَی الْأَرْبَعِ فَسَلِّمْ وَ انْصَرِفْ وَ إِنِ اعْتَدَلَ وَهْمُکَ فَانْصَرِفْ وَ صَلِّ رَکْعَتَیْنِ وَ أَنْتَ جَالِسٌ

📚 Al-Kafi, vol.3, p.353

Imam al-Sadiq (peace be upon him) said: When you do not know whether you have prayed three rak‘ahs or four, and your opinion falls on three rak‘ahs, then base it on three and add another rak‘ah. If your opinion falls on four, then give salām and complete the prayer. If your doubt is equal, then give salām and complete the prayer, and then pray two rak‘ahs sitting.

6 إِسْحَاقَ بْنِ عَمَّار قَالَ: قَالَ أَبُو عَبْدِ اللَّهِ إِذَا ذَهَبَ وَهْمُكَ إِلَى التَّمَامِ أَبَداً فِي كُلِّ صَلَاةٍ فَاسْجُدْ سَجْدَتَيْنِ بِغَيْرِ رُكُوعٍ أَفَهِمْتَ قُلْتُ نَعَمْ

📚 Al-Tahdhib, vol.2, p.183

Ishaq ibn ‘Ammar said: Imam al-Sadiq (peace be upon him) said: If in any prayer your doubt leans toward the prayer being complete, then perform two prostrations without bowing (i.e., two prostrations of forgetfulness). Do you understand? I said: Yes.

✅ From the above narrations it is clear that:

✅ If someone in a four-rak‘ah prayer doubts between three and four and his assumption leans more toward three rak‘ahs, he bases it on three rak‘ahs and prays one more.

✅ If his assumption leans more toward four rak‘ahs, he bases it on four, completes the prayer, and performs two prostrations of forgetfulness.

✅ If his doubt is equal, he bases it on four rak‘ahs and completes the prayer, and then either prays two rak‘ahs sitting with only al-Hamd or prays one rak‘ah standing with only al-Hamd.

✅ The ruling for one who doubts excessively is specific and was explained in Question 512.

✅ Pray for relief (faraj) ✅