It is narrated from Sayyiduna Zayd bin Arqam (may Allah be pleased with him); he said: I saw the Messenger of Allah (peace and blessings be upon him) supplicating; he (peace and blessings be upon him) raised both his hands so high that I saw the whiteness of his (peace and blessings be upon him) armpits.
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4965