✅Answer: Please study the following narrations:

عَنْ أَبِي بَصِيرٍ عَنْ أَبِي عَبْدِ اللَّهِ قَالَ: إِذَا رَفَعْتَ رَأْسَكَ مِنَ الرُّكُوعِ فَأَقِمْ صُلْبَكَ فَإِنَّهُ لَا صَلَاةَ لِمَنْ لَا يُقِيمُ صُلْبَهُ

📚Al-Kafi, Vol. 3, p. 320

Translation: Imam Sadiq (peace be upon him) said: 'When you raise your head from bowing, straighten your back, for the one who does not straighten his back (after bowing), there is no prayer for him.'

أَبِي بَصِيرٍ عَنْ أَبِي عَبْدِ اللَّهِ قَالَ: إِذَا رَفَعْتَ رَأْسَكَ مِنَ الرُّكُوعِ فَأَقِمْ صُلْبَكَ حَتَّى تَرْجِعَ مَفَاصِلُكَ

📚Al-Tahdhib, Vol. 2, p. 325

Translation: Imam Sadiq (peace be upon him) said: 'When you raise your head from bowing, straighten your back until your joints return (to their place).'

عن الصادق فی حدیث :مَا أَشَدُّ مِنْ سَرِقَةِ الصَّلَاةِ فَإِذَا قَامَ أَحَدُكُمْ فَلْيَعْتَدِلْ وَ إِذَا رَكَعَ فَلْيَتَمَكَّنْ وَ إِذَا رَفَعَ رَأْسَهُ فَلْيَعْتَدِلْ

📚Qurb al-Isnad, p. 18

Translation: Imam Sadiq (peace be upon him) said in a hadith: 'What is more severe than stealing from the prayer! So when one of you (stands in prayer), he should stand completely straight, and when he bows, he should be calm (in the bowing position), and when he raises his head from bowing, he should straighten and align himself.'

عن الصادق فی حدیث حماد :ثُمَّ سَبَّحَ ثَلَاثاً بِتَرْتِيلٍ وَ قَالَ سُبْحَانَ رَبِّيَ الْعَظِيمِ وَ بِحَمْدِهِ- ثُمَّ اسْتَوَى قَائِماً فَلَمَّا اسْتَمْكَنَ مِنَ الْقِيَامِ قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ- ثُمَّ كَبَّرَ وَ هُوَ قَائِمٌ وَ رَفَعَ يَدَيْهِ حِيَالَ وَجْهِهِ وَ سَجَدَ

📚Man La Yahduruhu al-Faqih, Vol. 1, p. 300

Translation: Hammad ibn Isa narrated in the description of the prayer of Imam Sadiq (peace be upon him): '...Then he said the glorification three times and said:

سُبْحَانَ رَبِّيَ الْعَظِيمِ وَ بِحَمْدِهِ

Then he stood completely straight, and when he was calm in the standing position, he said:

سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ

Then he said the takbir while still standing and raised his hands for the takbir to face his face and went into prostration...'

✅In several hadiths, a few of which were mentioned, the Ahl al-Bayt (peace be upon them) have instructed us regarding the manner of prayer to stand completely straight after bowing until our back is straightened and our joints return to their normal state, and after saying 'Sami'a Allahu liman hamidah' and also saying 'Allahu Akbar,' we should go into prostration. According to the above narration, for the one who does not straighten his back after bowing, there is no prayer for him. We should not go directly into prostration after finishing the bowing, or only straighten our back slightly and go into prostration. Rather, we are obligated to straighten our back completely and, after being calm and saying the prescribed remembrances, go into prostration.

✅It is worth mentioning that there are many other pieces of evidence for the necessity of this act in prayer, many of which are mentioned in the context of other rulings of prayer in the narrations.

✅Note: Please pay attention to the following narration:

عَنْ جَابِرٍ عَنْ أَبِي جَعْفَرٍ قَالَ: سَارِعُوا فِي طَلَبِ الْعِلْمِ فَوَ الَّذِي نَفْسِي بِيَدِهِ لَحَدِيثٌ وَاحِدٌ فی حلال و حرام تَأْخُذُهُ عَنْ صَادِقٍ خَيْرٌ مِنَ الدُّنْيَا وَ مَا حَمَلَتْ مِنْ ذَهَبٍ وَ فِضَّةٍ

📚Al-Mahasin, p. 227

Translation: Imam Baqir (peace be upon him) said: 'Hasten in seeking knowledge. By the One in Whose hand is my soul, indeed, a single hadith that you take from a truthful person about the lawful and the unlawful of Allah is better than the whole world and all the gold and silver in it.'

✅Note that after encouraging the seeking of knowledge, he also introduced its way, which is: 'to learn the hadiths of the Ahl al-Bayt (peace be upon them) from truthful people and, if Allah wills, to act upon them.'

✅Let's hasten and be quick according to the command of Imam Baqir (peace be upon him) and align all our religious affairs with the teachings of the Ahl al-Bayt (peace be upon them) and not exchange the pleasure of acting directly upon the commands and orders of the Commander of the Faithful and his pure children with anything else, and to go so far as to become an example of this saying of our master:

The Imam of the Pious, the Commander of the Faithful (peace be upon him), said in his will to Kumayl ibn Ziyad:

یَا کُمَیْلُ لَا تَأْخُذْ إِلَّا عَنَّا تَکُنْ مِنَّا

'O Kumayl, do not take (the rulings of your religion) from anyone but us, the Ahl al-Bayt, so that you may be from us.'

📚Bisharat al-Mustafa, p. 30