Musannaf Ibn Abi Shayba 26:51

Waki’ narrated to us, from Sufyan, from al-A’mash, from Ibrahim, from Masruq, who said: He arrived, and ‘Alqama said to him: "Was Ibn Mas’ud not firm (in his knowledge)?" Masruq said to him: "Nay, but I saw Zayd ibn Thabit and the people of Medina associating (others with Allah in their opinions/judgments)."