It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he would raise both hands when beginning the prayer, also when going into the bowing, and also when he stood up straight after rising from the bowing (at all of these points he raised his hands up to his shoulders), and he would say that the Messenger of Allah (peace and blessings be upon him) used to do this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2511