It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that when the Messenger of Allah (peace and blessings be upon him) entered into the prayer, he would raise his hands up to his shoulders, and when he bowed or raised his head from bowing, he would also do 'raf' al-yadayn' (raising the hands).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2302