Musnad Ahmad 658:230

'Abd al-Razzaq narrated to us, Sufyan informed us, from Yazid ibn Abi Ziyad, from 'Abd al-Rahman ibn Abi Layla, from al-Bara' ibn 'Azib, who said: "When the Prophet, peace and blessings of Allah be upon him, would say the takbir, he would raise his hands until we could see his thumbs near his ears."