Musnad Abu Ya'la al-Mawsili 155:145

'Abd al-Ghaffar ibn 'Abd Allah ibn al-Zubayr narrated to us, 'Ali ibn Mushir narrated to us, from Muhammad ibn 'Amr, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) saw a man praying while the mu'adhdhin was performing the iqamah. The Messenger of Allah (may Allah bless him and grant him peace) said to him: "Are there two prayers together?"