It is narrated that Ahmed ibn Hanbal said,
"if in any matter there is agreement between three people, then one pays no attention to the verdict of anyone who disagrees with them."

Someone asked him, "who are they?"

He answered, "Abu Hanifah, Abu Yusuf and Muhammad ibn al-Hasan. Abu Hanifa is the one with most insight with respect to analogical reasoning. Abu Yusuf is the one with the most insight with respect to the traditions. Muhammad is the one with most insight with respect to Arabic."

As-Samani narrated it in kitab al-ansab.