✅Answer: Please pay attention to the following narrations:

زُرَارَةَ قَالَ: سَأَلْتُ أَبَا جَعْفَرٍ عَنِ الْفَرْضِ فِي الصَّلَاةِ فَقَالَ الْوَقْتُ وَ الطَّهُورُ وَ الْقِبْلَةُ وَ التَّوَجُّهُ وَ الرُّكُوعُ وَ السُّجُودُ وَ الدُّعَاءُ قُلْتُ مَا سِوَى ذَلِكَ فَقَالَ سُنَّةٌ فِي فَرِيضَةٍ

📚Al-Tahdhib, Vol. 2, p. 241

Zurara said: 'I asked Imam Baqir (peace be upon him) about the obligatory parts of prayer.' The Imam said: 'The time, purification, the qibla, the 'tawajjuh' (turning), bowing, prostration, and supplication.' I said: 'What are the others?' He said: 'A recommended act in the obligatory one.'

✅In the above narration, 'tawajjuh' is introduced as one of the obligatory parts of prayer. To understand what 'tawajjuh' is, please pay attention to the following narrations:

زُرَارَةَ قَالَ: أَدْنَى مَا يُجْزِئُ مِنَ التَّكْبِيرِ فِي التَّوَجُّهِ تَكْبِيرَةٌ وَاحِدَةٌ وَ ثَلَاثُ تَكْبِيرَاتٍ أَحْسَنُ وَ سَبْعٌ أَفْضَل

📚Al-Kafi, Vol. 3, p. 310

Translation: Zurara said: '(Imam Baqir, peace be upon him, said): 'The minimum amount of 'takbir' that suffices in 'tawajjuh' is one takbir, and three takbirs are better, and seven takbirs are most excellent.'

زُرَارَةَ عَنْ أَبِي جَعْفَرٍ قَالَ: يُجْزِئُكَ فِي الصَّلَاةِ مِنَ الْكَلَامِ فِي التَّوَجُّهِ إِلَى اللَّهِ....

Imam Baqir (peace be upon him) said: 'In prayer, for the words in 'tawajjuh' towards Allah, it suffices for you to say:

وَجَّهْتُ وَجْهِيَ لِلَّذِي فَطَرَ السَّماواتِ وَ الْأَرْضَ عَلَى مِلَّةِ إِبْرَاهِيمَ حَنِيفاً مُسْلِماً وَ ما أَنَا مِنَ الْمُشْرِكِينَ- إِنَّ صَلاتِي وَ نُسُكِي وَ مَحْيايَ وَ مَماتِي لِلَّهِ رَبِّ الْعالَمِينَ لا شَرِيكَ لَهُ وَ بِذلِكَ أُمِرْتُ وَ أَنَا مِنَ الْمُسْلِمِينَ

📚Al-Tahdhib, Vol. 2, p. 67

✅From the two above hadiths, it is clear that the 'takbirat al-ihram' (the opening takbir) of the prayer and also the supplication 'wajjahtu wajhi' are part of the 'tawajjuh.' But are both of these obligatory or not? To answer this question, please pay attention to the following hadith, among others:

Imam Mahdi (peace be upon him) in his response to Himyari who asked about 'tawajjuh,' replied:

التَّوَجُّهُ كُلُّهُ لَيْسَ بِفَرِيضَةٍ وَ السُّنَّةُ الْمُؤَكَّدَةُ فِيهِ الَّتِي كَالْإِجْمَاعِ الَّذِي لَا خِلَافَ فِيهِ

Translation: 'Tawajjuh' is not all obligatory, and the confirmed sunnah in it (which is like a consensus in which there is no disagreement) is that you say:

وَجَّهْتُ وَجْهِيَ لِلَّذِي فَطَرَ السَّمَاوَاتِ وَ الْأَرْضَ حَنِيفاً مُسْلِماً عَلَى مِلَّةِ إِبْرَاهِيمَ وَ دِينِ مُحَمَّدٍ وَ هَدْيِ عَلِيٍّ أَمِيرِ الْمُؤْمِنِينَ وَ مَا أَنَا مِنَ الْمُشْرِكِينَ إِنَّ صَلاتِي وَ نُسُكِي وَ مَحْيايَ وَ مَماتِي لِلَّهِ رَبِّ الْعالَمِينَ لا شَرِيكَ لَهُ وَ بِذلِكَ أُمِرْتُ وَ أَنَا مِنَ الْمُسْلِمِينَ اللَّهُمَّ اجْعَلْنِي مِنَ الْمُسْلِمِينَ أَعُوذُ بِاللَّهِ السَّمِيعِ الْعَلِيمِ مِنَ الشَّيْطَانِ الرَّجِيمِ- بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ

Then you recite Surah Al-Hamd.

📚Al-Ihtijaj, p. 486

Also, pay attention to the following narration:

زُرَارَةَ قَالَ: سَأَلْتُ أَبَا جَعْفَرٍ عَنْ کِبَارِ حُدُود الصَّلَاةِ فَقَالَ سَبْعَةٌ الْوُضُوءُ وَ الْوَقْتُ وَ الْقِبْلَة وَ تَکْبِیرَةُ الِافْتِتَاحِ وَ الرُّکُوعُ وَ السُّجُودُ وَ الدُّعَاء

📚Mustadrak, Vol. 3, p. 98

Translation: Zurara said: 'I asked Imam Baqir (peace be upon him) about the major limits of prayer.' The Imam said: 'There are seven: ablution, time, the qibla, the takbirat al-iftitah (opening takbir), bowing, prostration, and supplication.'

✅The above narration is like the first narration except that instead of 'tawajjuh,' it says 'takbirat al-iftitah.'

✅It is clear that the obligatory 'tawajjuh' is the same as the 'takbirat al-ihram,' and the supplication 'wajjahtu wajhi' is the words in 'tawajjuh' which is introduced as a 'sunnah.' And the assumption of those who have thought that the obligatory 'tawajjuh' is the supplication 'wajjahtu wajhi' and based on that, consider this supplication to be obligatory, is a great mistake. Many pieces of evidence can be presented to show that this supplication is not obligatory but a confirmed sunnah, and according to the narration in Al-Ihtijaj above and the narration in 📚Al-Kafi, Vol. 3, p. 310, and other narrations, its place is after the 'takbirat al-ihram' and before Surah Al-Hamd.

✅In the famous narration of Fadl ibn Shadhan, who narrates the reasons for the rulings from Imam Ridha (peace be upon him) in the first volume of 📚Ilal al-Shara'i, p. 265, he explicitly states the obligatoriness of the 'takbirat al-ihram,' which is a witness to the narration of the obligatory parts of prayer, one of which is 'tawajjuh' or the opening of the prayer and the 'takbirat al-ihram.'

✅'Tawajjuh' is placed among the 'obligatory parts of prayer' in the hadith in 📚Al-Khisal, Vol. 2, p. 604, meaning that 'tawajjuh' is obligatory in all prayers, which is the 'takbirat al-ihram,' while the supplication 'wajjahtu wajhi' is placed among the sunnahs of the six prayers in the hadith in 📚Bihar, Vol. 84, p. 360, and others.

✅There are other reasons as well for the supplication 'wajjahtu wajhi' not being obligatory, which are omitted due to message limitations.