At the time, Khurasan, at-Tirmidhi’s native land, was a major learning centre, home to many muhaddiths. Other significant learning centres visited by at-Tirmidhi were the Iraqi cities of Kufa and Basra. At-Tirmidhi reported hadith from 42 Kufan teachers. In his Jami`, he used more reports from Kufan teachers than from teachers of any other town.
At-Tirmidhi was a pupil of al-Bukhari who was based in Khurasan. Adh-Dhahabi wrote, “His knowledge of hadith came from al-Bukhari.” At-Tirmidhi mentioned al-Bukhari’s name 114 times in his Jami`. He used al-Bukhari’s Kitab at-Tarikh as a source when saying discrepancies in the text of a hadith or its transmitters. He praised al-Bukhari as being the most knowledgeable person in Iraq or Khurasan in the science of discrepancies of hadith. When mentioning the rulings of jurists, he followed al-Bukhari’s practice of not saying the name of Abu Hanifah. Because he never received a reliable chain of narrators mentioning Abu Hanifa’s decrees, he would attribute them to “some people of Kufa.” Al-Bukhari held at-Tirmidhi in high regard. He is reported to have told at-Tirmidhi, “I have profited more from you than you have from me,” in his Sahih, he narrated two hadith from at-Tirmidhi.

At-Tirmidhi also narrated some hadiths from Abu Dawud and one from Muslim. Muslims also narrated one hadith from at-Tirmidhi in his own Sahih.

A.J. Wensinck mentions Ahmad ibn Hanbal as among at-Tirmidhi’s teachers. However, Hoosen states that according to the most reliable sources, at-Tirmidhi never went to Baghdad, nor did he attend any lectures of Ahmad ibn Hanbal. Furthermore, at-Tirmidhi never directly narrates from Ahmad ibn Hanbal in his Jami`. Several at-Tirmidhi’s teachers also taught al-Bukhari, Muslim, Abu Dawud, Ibn Majah, and an-Nasa’i.
 
https://en.wikipedia.org/wiki/Al-Tirmidhi