Musannaf Ibn Abi Shayba 23:95

Abu Mu'awiyah narrated to us, from Yusuf ibn Maymun, who said: I said to 'Ata', "There are people among us whom we consider to be among the righteous. If we say, 'We are believers,' they criticize that against us." He said: So 'Ata' said, "We are the Muslims, the believers; and that is how we found the companions of Muhammad, may Allah bless him and grant him peace, saying."