Musnad Ahmad 30:1309

'Abd al-Samad narrated to us, 'Abd al-'Aziz narrated to us, Isma'il—meaning Ibn Abi Khalid—narrated to us, from his father, who said: I said to Abu Hurayrah, "Is this how the Messenger of Allah, peace and blessings of Allah be upon him, used to pray with you?" He said, "And what did you disapprove of in my prayer?" He said: I said, "I wanted to ask you about that." He said, "Yes, and be brief." He said: "His standing was [for] the duration of the time it takes for the mu'adhdhin to descend from the minaret and reach the row."