Musnad Abu Ya'la al-Mawsili 115:125

Abu Khaythama narrated to us, Yahya narrated to us, from Ibn Abi Arubah, from Qatadah, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) would not raise his hands in any supplication except in the prayer for rain (Istisqa). For indeed, he would raise his hands until the whiteness of his armpits could be seen.