Musannaf Ibn Abi Shayba 3:2391

Ibn ‘Ulayyah narrated to us, from ‘Abbad ibn Mansur, who said: I arrived at the congregational mosque while I was of the opinion that they had not yet prayed Dhuhr, so I stood up to perform voluntary prayer until the prayer was established. When they prayed, it turned out to be ‘Asr. So I stood up and prayed Dhuhr with them, then I prayed ‘Asr. Then I came to al-Hasan and mentioned that to him, and he commanded me [to do] the like of what I had done.