Musannaf Ibn Abi Shayba 3:3363

Marwan ibn Mu'awiyah narrated to us, from Isma'il ibn Sami', from 'Ali ibn Abi Kathir, that Abu Mas'ud al-Ansari, when it was the day of Adha or the day of Fitr, would walk among the rows and say: "There is no prayer except with the Imam."