He is unanimously regarded as the Ameerul Mu'mineen in the field of Hadith and Imams Buhkari(R) & Muslim(R) narrate many Hadith from him.
He was one of the special students of Imam Abu Hanifa(R) and was so captivated by the personality of Imam Abu Hanifa(R) that he stayed with him through out his life. He had the following to say about Imam Abu Hanifa(R)
"I have been to Many Cities but I had never known the principles of Halal & Haram until I met him (Imam Abu Hanifa(R))"
"I have studied under many teachers, but I had never known any as proficient in Fatawa as he (Imam Abu Hanifa(R))"
"Were it not for sounding prejudiced, I would say that I have never seen anyone as proficient in Fatawa as he (Imam Abu Hanifa(R))"
"He (Imam Abu Hanifa(R)) excelled people in his momery for Hadith, his Fiqh, his knowledge, his trustworthiness and his sheer piety"
"He had the deepest understanding of Deen and I have never seen any with a deeper understanding than he"
"If an opinion is to be sought, it is to be taken from Malik, Sufyan and Abu Hanifa (R). From them, the one with the best, the deepest and most finely tuned understanding is Abu Hanifa(R)"
"There is none worthy of being followed than Imam Abu Hanifa(R) because he was an Imam, a pious man, an Alim, and a Faqih. With his keen insight, understanding and intelligence, he has exposed knowledge in such a way that no other has done
SubhanAllah, the last comment reminds me of the Hadith about the Persians and the furthest planet.
Manaaqib Kurdi (Vol1 Pg. 103 & 104)
Jaami Bayaanil Ilm Pg. 113
Kharatul Hisaan Pg. 29