It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both): I saw the Messenger of Allah (peace and blessings be upon him). When he (peace and blessings be upon him) began the prayer, he said the takbir and also raised his hands until he brought his hands level with his shoulders. Then when he bowed, he did the same. Then when he said 'Sami' Allahu liman hamidah' (Allah hears the one who praises Him), he also did the same, and he said 'Rabbana wa lakal-hamd' (Our Lord, and to You belongs all praise). He did not raise his hands like this in the prostrations.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2506