Description of standing upright after bowing and the supplications recited in it:
The Prophet (may Allah bless him and give him peace), when he raised his back from bowing, would say:

“Samʿa Allahu liman ḥamidah” (Translation: Allah, the Exalted, hears the one who praises Him). As you instructed:
“No one’s prayer is complete until he says ‘Allahu akbar,’ then bows, then says ‘Samʿa Allahu liman ḥamidah’ and stands up properly.”
And when you raised your head from bowing, you would stand so straight that all the bones of your spine returned to their places. In this position you would say:

“Allāhumma Rabbanā Laka Al-Ḥamd”
Translation:
O Allah Our Lord, to You alone belongs praise.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ ، ‏‏‏‏‏‏عَنْ مَالِكٍ ، ‏‏‏‏‏‏عَنْ نُعَيْمِ بْنِ عَبْدِ اللَّهِ الْمُجْمِرِ ، ‏‏‏‏‏‏عَنْ عَلِيِّ بْنِ يَحْيَى بْنِ خَلَّادٍ الزُّرَقِيِّ ، ‏‏‏‏‏‏عَنْأَبِيهِ ، ‏‏‏‏‏‏عَنْ رِفَاعَةَ بْنِ رَافِعٍ الزُّرَقِيِّ ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ كُنَّا يَوْمًا نُصَلِّي وَرَاءَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ، ‏‏‏‏‏‏فَلَمَّا رَفَعَ رَأْسَهُ مِنَ الرَّكْعَةِ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ، ‏‏‏‏‏‏قَالَ رَجُلٌ وَرَاءَهُ:‏‏‏‏ رَبَّنَا وَلَكَ الْحَمْدُ حَمْدًا كَثِيرًا طَيِّبًا مُبَارَكًا فِيهِ، ‏‏‏‏‏‏فَلَمَّا انْصَرَفَ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ مَنِ الْمُتَكَلِّمُ ؟ قَالَ:‏‏‏‏ أَنَا، ‏‏‏‏‏‏قَالَ:‏‏‏‏ رَأَيْتُ بِضْعَةً وَثَلَاثِينَ مَلَكًا يَبْتَدِرُونَهَا أَيُّهُمْ يَكْتُبُهَا أَوَّلُ.
Narrated by Abdullah ibn Maslama, from Mālik, from Nuʿaym ibn Abdullah al-Mujmir, from ʿAli ibn Yaḥyā ibn Khallād al-Zuraqī, from his father, from Rifāʿah ibn Rāfiʿ al-Zuraqī, who said:
“One day we were praying behind the Prophet (may Allah bless him and give him peace). When he raised his head from bowing, he said:

‘Samʿa Allahu liman ḥamidah.’
A man behind him said:

‘Rabbana wa laka al-ḥamd, ḥamdan kathīran ṭayyiban mubārakan fīh’
(Our Lord, and to You is all praise, abundant, pure, and blessed).
When the Prophet (may Allah bless him and give him peace) finished the prayer, he asked:
‘Who spoke?’ The man replied: ‘I did.’ He said:
‘I saw more than thirty angels racing to record it, to see which of them would write it down first.’”
(Sahih al-Bukhari, 799)