Musnad Ahmad 1153:1020

Waki’ narrated to us, from Sufyan, from Hakim ibn Jubayr, from Ibrahim, from al-Aswad, from ‘Aishah, who said: "I have not seen anyone who was more prompt in performing the Dhuhr prayer than the Messenger of Allah (may Allah bless him and grant him peace), nor Abu Bakr, nor ‘Umar."