Ibn Abu Yala al-Hanbali in “Tabaqatul Hanabila” (1/29, thk Abdurrahman al-Uthaymeen) wrote:

“Rabia ibn Sulaiman narrated that Imam Shafei said: Who hates Ahmad ibn Hanbal is kaafir. I asked: You implement upon him name of disbeliever? Imam Shafei said: Yes, who hates Ahmad ibn Hanbal he opposes Sunnah. And who opposes sunnah targeted companions, and who targeted companions hates prophet (sallalahu alaihi wa ala alihi wa sallam), and who hates him is disbeliever in Great Allah”.