It is narrated from Sa'id bin Jubayr (may Allah have mercy on him) that someone asked him about raising the hands in the prayer, and he said: It is something by which a man adorns his prayer.
The Companions of the Messenger of Allah (peace and blessings be upon him) (may Allah be pleased with them) used to raise their hands when beginning the prayer, and also at the bowing and when raising their heads from the bowing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2525