Part 1 | Part 2
The incident that directed Abu Hanifah to frequenting the scholars is narrated by all of his biographers. He recounts the incident himself:
“One day, I passed by [`Amir] al-Sha`bi who was seated. He called me and asked: “Where do you go?”
I named a merchant whom I was going to see.
“I did not mean [your going to] the market,” al-Sha`bi said. “Rather, I meant which scholars you go to.”
I said: “I hardly ever attend any (of their classes).”
Then Sha`bi said: “You ought to study knowledge [i.e. of the religion] and sit in the company of learned men. I discern signs of intelligence and energy in you.”
His advice struck my heart, and I left off turning to the market, and turned to learning. Thus, God, Exalted is He, benefitted me by his advice.”
Al-Sha`bi was a prominent tabi`i and among the most senior of Abu Hanifah’s teachers. Following his encounter with al-Sha`bi, Abu Hanifah immersed himself in the circles of knowledge.
Based on some reports, it is related that he started off his scholarly pursuit engaging in kalam (dogma/theology). He travelled to Basra often for business related matters where he was exposed to a lot of the rhetoric-revolving kalam.
Basrah was a bustling city with a diverse range of sects and viewpoints. Abu Hanifah found himself busy debating and refuting various groups and sects, namely the Kharijis. These debates played an important role in developing some of Abu Hanifah’s skills. Dr. Akram Nadwi states, “He acquired a general reputation for sharpness and brilliance in such debates.”
As time passed and his understanding matured, he left kalam and began to study fiqh under the eminent scholar, Hammad ibn Abi Sulayman al-Kufi. This change of interest took place from an apparent realization that he had gone through—in order to benefit the general body of Muslims, fiqh was the way forward.
Abu Zahra states that there is no way we can find out the exact age when Abu Hanifah began his studies with Hammad ibn Abi Sulayman. However, what is known is that he remained with Hammad until his death. 
Conversely, Dr. Akram Nadwi actually gives an estimate of how old Abu Hanifah was when he started his learning. According to him, Abu Hanifah stayed with Hammad for 18 years until the latter passed away in 120 A.H. Abu Zahra cites a report mentioning this as well. From this, we are able to calculate that when Abu Hanifah joined Hammad’s school he was twenty-two years old. Although he studied with other teachers, there is no doubt that Abu Hanifah received his training mainly from Hammad.
Abu Hanifah performed Hajj and visited Makkah and Madinah numerous times. The two holy mosques in Makkah and Madinah served as a focal point for scholars from different parts of the Islamic world to meet, learn, and exchange ideas. Abu Hanifah would take advantage of his time in the two mosques and benefit from the scholars that he would meet there.
He studied under many of the tabi`in and from among the eminent scholars of his time. He studied both fiqh and Hadith with teachers of the highest caliber. According to one estimate he narrated Hadiths from about 300 different teachers, a considerable amount of them are recognized as leaders in the field of Hadith.
This indicates that he was indeed well versed in the sunnah, contrary to what some of his detractors claim. It is also important to note that he studied with all the famous authorities of his time, and that these authorities were also the teachers of Sufyan al-Thawri, of al-Awza`i, of Malik ibn Anas, and of Layth ibn Sa`d.
The Hadiths narrated by 74 of Abu Hanifah’s teachers are recorded in the Six Books, the compilations of Hadiths that became widely established as the most sahih or reliable, that is, the collections of: Bukhari, Muslim, Tirmizi, Abu Dawud, Nasa’i, and Ibn Majah.
Dr. Nadwi provides a survey and biographical description of some of the teachers of Abu Hanifah who were regarded as Imams in fiqh and Hadith. To point out a few of scholars he listed: `Amir al-Sha`bi, `Ata’ ibn Abi Rabah, Abu Bakr Muhammad ibn Muslim ibn Shihab al-Zuhri, `Amr ibn Dinar al-Makki, Qatadah ibn Di`amah al-Sadusi al-Basri, and others.
It is important to note that for fiqh, the derivation of laws, and for his methods of reasoning, he relied above all and most assiduously on Hammad ibn Abi Sulayman. He was so loyal to Hammad to the extent that he never left his company. He did not conduct his own classes out of respect for his beloved teacher. It was only after Hammad’s death did he succeed him as the principal teacher of fiqh in Kufah and begin to conduct classes. By that time his fame spread far and wide. Experts of fiqh and Hadith attended his sessions, and people from every major city in the Islamic world came to study with him.