My father said, "Messenger of Allah ﷺ used to raise both his hands up to the level of his shoulders when opening the prayer; and on saying the Takbir for bowing. And on raising his head from bowing he used to do the same and then say "Samiʿa l-lahu liman hamidah, Rabbana wa laka l-hamd." And he did not do that (i.e. raising his hands) in prostrations. (Using translation from Bukhārī 735)  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا افْتَتَحَ الصَّلَاةَ رَفَعَ يَدَيْهِ حَذْوَ مَنْكِبَيْهِ وَإِذَا كَبَّرَ لِلرُّكُوعِ وَإِذَا رَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ رَفَعَهُمَا كَذَلِكَ أَيْضًا وَقَالَ «سَمِعَ اللهُ لِمَنْ حَمِدَهُ رَبِّنَا وَلَكَ الْحَمْدُ» وَكَانَ لَا يَفْعَلُ ذَلِكَ فِي السُّجُودِ  

"When the Prophet ﷺ raised his head from bowing, he said: 'Allahumma Rabbana wa lakal-hamd (O Allah, our Lord and to You be the praise).'" (Using translation from Nasāʾī 1060)  

كَانَ رَسُولُ اللهِ ﷺ إِذَا رَفَعَ رَأْسَهُ مِنَ الرَّكْعَةِ قَالَ «اللهُمَّ رَبِّنَا وَلَكَ الْحَمْدُ»