Musannaf Ibn Abi Shayba 13:3032

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from al-A'mash, from 'Umarah, from 'Abd al-Rahman ibn Yazid, who said: They spoke much to 'Abdullah one day, so he said: "O people, a time has come upon us when we were not judging, and we were not in that position. Then, Allah has seen of the matter what you see. So whoever among you is presented with a judgment after today, let him judge by what is in the Book of Allah. If a matter comes to him that is not in the Book of Allah, let him judge by what His Prophet, may Allah bless him and grant him peace, judged. If a matter comes to him that is not in the Book of Allah and the Prophet, may Allah bless him and grant him peace, did not judge by it, let him judge by what the righteous have judged. If a matter comes to him that is not in the Book of Allah, and the Messenger of Allah, may Allah bless him and grant him peace, did not judge by it, and the righteous did not judge by it, let him exert his own opinion, and let him not say, 'I think,' and 'I fear.' For the lawful is clear and the unlawful is clear, and between them are doubtful matters; so leave what makes you doubt for what does not make you doubt."