Why did the four Imams forbid their emulation and condemn those who adopted their sayings without proof?

The Imams forbade their students from blindly following them for several reasons, including: their knowledge that the Sunnah of the Messenger of Allah, peace and blessings be upon him, might be hidden from them; the changing of their own opinions and ijtihad (independent reasoning); and their concern that their sayings should not contradict the legal texts. Each of Imam Al-Shafi'i, Ahmad, Abu Hanifa, and Malik emphasized giving precedence to the saying of the Messenger of Allah, peace and blessings be upon him, and to the legal proofs over their own sayings, and that they are human beings who err and are correct. Nevertheless, this prohibition is directed at scholarly mujtahids (those capable of independent reasoning), whereas the common people must follow trustworthy scholars, as Allah the Almighty says: "So ask the people of the Reminder if you do not know."