It is well known that Imam al-Sadiq (as) had thousands of students. Thus, it makes sense that many were not Shia or followers of Ahl al-Bayt. Moreover, because our Imam was teaching foundational concepts of Islam (kalam, hadith, seerah), many flocked to him to learn. Thus, it is accepted that he taught Abu Hanifa and Malik ibn Anas; Hanbal and al-Shafii came a little later. There are many Sunni and Shia sources that point to these details.

Some information can be found here (please note, I am not endorsing this site, but the basic information here shows want is known):

http://www.shiapen.com/comprehensive/students-of-imam-jafar/proving-teacher-student-relationship.html