Musnad Ahmad 1007:71

Ya'la narrated to us, Hajjaj al-Sawwaf narrated to us, from Yahya ibn Abi Kathir, from Abdullah ibn Abi Qatadah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When the prayer is called (iqamah), do not stand up until you see me."