Nafi' said: When Ibn Umar (may Allah be pleased with them both) began the prayer, he would say the takbir and raise his hands; when he bowed, he would also raise his hands; when he said 'Sami'a Allahu liman hamidah' (Allah has heard the one who praised Him), he would also raise his hands; and when he stood up from two rak'ahs, he would also raise his hands. And Ibn Umar (may Allah be pleased with them both) narrated this hadith as marfu' (attributed) to the Prophet (peace and blessings be upon him).
Abd al-A'la is alone in attributing it to the Prophet (peace and blessings be upon him), and he is thiqah (trustworthy).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2814