Musnad Abu Ya'la al-Mawsili 152:97

And from al-A'mash, from Abu Wa'il, from 'Abdullah, who said: I prayed with the Messenger of Allah (may Allah bless him and grant him peace), and he prolonged [the prayer] until I intended to do a bad thing. He said: "And what did you intend to do?" He said: "I intended to sit down and leave him."