Musnad Ahmad Hadith 6175

It is narrated from Ibn Umar (may Allah be pleased with them both) that when the Prophet (ﷺ) would stand for prayer, he would raise his hands so much that they would be at the level of his shoulders, then he would say the takbeer. When he would go into bowing (ruku'), he would again raise his hands so much that they would be at the level of his shoulders, then he would say the takbeer and go into ruku'. When he wanted to raise his back (from ruku'), he would again raise his hands so much that they would be at the level of his shoulders and say "Sami' Allahu liman hamidah" and go into prostration (sajdah), but he would not raise his hands in prostration. However, in every rak'ah and before every takbeer for ruku', he would raise his hands until the prayer was completed.