Musnad Ahmad 1012:14

Sufyan narrated to us, from Yahya, from Ubadah ibn al-Walid ibn Ubadah ibn al-Samit, that he heard it from his grandfather. And Sufyan said once: From his grandfather, Ubadah. Sufyan said: And Ubadah was a Naqib (chieftain), and he was one of the seven. He said: "We pledged allegiance to the Messenger of Allah, may Allah bless him and grant him peace, to hear and obey in hardship and ease, and in what we like and what we dislike, and that we would not dispute the authority of those who hold it, and that we would speak the truth wherever we are, not fearing for the sake of Allah the blame of any critic." Sufyan said: Some people added: "Unless you see open disbelief."