Musannaf Ibn Abi Shayba 3:1621

Abu Mu'awiyah narrated to us, from Abd al-Rahman ibn Ishaq, from Ziyad ibn Zayd al-Sawa'i, from Abu Juhayfah, from Ali, who said: "Indeed, it is from the Sunnah in the obligatory prayer, when a man rises in the first two rak'ahs, that he should not lean with his hands upon the ground, unless he is an old man who is unable [to do otherwise]."