Wakee' and Hafs ibn Ghiyaath said, "None has come to Koofah the like of that youth," meaning Ahmad ibn Hanbal. Yahyaa ibn Aadam said, "Ahmad ibn Hanbal is our Imaam."
Ibn Raahawaih said, "I used to sit with Ahmad and ibn Ma'een and we would revise ahaadeeth. I would say, "What is the Fiqh of it? What is its explanation?" And they would be silent- except Ahmad."
'Abdur-Rahmaan ibn Mahdee mentioned the companions of hadeeth and said, "The most knowledgable of them regarding the ahaadeeth of ath-Thawree is Ahmad ibn Hanbal." Then Ahmad entered and ibn Mahdee said, "Whosoever wished to see that which was held between the shoulders of ath-Thawree, then let him look at this man."
'Abdur-Razzaq said, "I have not seen anyone having better knowledge and understandnig, nor more piety than Ahmad ibn Hanbal." Adh-Dhahabee adds, "he said this having seen the life of ath-Thawree, Maalik, and ibn Jurayj."
More to come insha'Allah...