✅Answer: Please pay attention to the following narrations:

1️⃣ Hammad ibn Isa narrated about the manner of Imam Sadiq's (peace be upon him) prayer, until he said:

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 سَجَدَ

Translation: Then the Imam recited the glorification slowly in the bowing and said three times:

سُبْحَانَ رَبِّيَ الْعَظِيمِ وَ بِحَمْدِهِ

Then he stood up straight, and when he was completely straight, he said:

سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ

Then, while standing, he raised his hands in front of his face and said the takbir and went into prostration.

📚Al-Faqih, Vol. 1, p. 300

2️⃣ Imam Sadiq or Imam Baqir (peace be upon them) said about the manner of the Prayer of Signs:

ثُمَّ تَرْكَعُ الْخَامِسَةَ فَإِذَا رَفَعْتَ رَأْسَكَ قُلْتَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ- ثُمَّ تَخِرُّ سَاجِداً فَتَسْجُدُ سَجْدَتَيْنِ

📚Al-Tahdhib, Vol. 3, p. 155

Translation: ...Then you perform the fifth bowing, and when you raise your head from bowing, you say:

سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ

Then you go into prostration and perform two prostrations....

3 مُحَمَّدُ بْنُ يَعْقُوبَ عَنْ مُحَمَّدِ بْنِ إِسْمَاعِيلَ عَنِ الْفَضْلِ بْنِ شَاذَانَ عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ جَمِيلِ بْنِ دَرَّاجٍ قَالَ: سَأَلْتُ أَبَا عَبْدِ اللَّهِ فَقُلْتُ مَا يَقُولُ الرَّجُلُ خَلْفَ الْإِمَامِ إِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ- قَالَ يَقُولُ الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ وَ يَخْفِضُ مِنَ الصَّوْتِ

📚Al-Kafi, Vol. 3, p. 320

Translation: Jamil said: 'I asked Imam Sadiq (peace be upon him) and said: 'What should a person who is behind the Imam say when the Imam says 'Sami'a Allahu liman hamidah'?' The Imam said: 'He should lower his voice and say:

الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ

4️⃣ Imam Sadiq (peace be upon him) used to say after raising his head (from bowing):

سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ الرَّحْمَنِ الرَّحِيمِ بِحَوْلِ اللَّهِ وَ قُوَّتِهِ أَقُومُ وَ أَقْعُدُ أَهْلِ الْكِبْرِيَاءِ وَ الْعَظَمَةِ وَ الْجَبَرُوتِ

📚Al-Dhikra, p. 199

✅According to Shi'a narrations, 'Sami'a Allahu liman hamidah' and similar supplications are said when raising the head from bowing, and the Ahl al-Bayt (peace be upon them) have not made a distinction between standing prayer and seated prayer. Therefore, saying 'Sami'a Allahu liman hamidah' and other remembrances that are mentioned in the hadiths for the time of raising the head from bowing are also said in seated prayer after raising the head from bowing.

✅According to the third hadith, when the Imam of the congregation says 'Sami'a Allahu liman hamidah' in congregational prayer, the followers say quietly:

الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ