“Shu’ba bin al-Hajjaj” who is amongst Shia opponents, says:

وشعبة من الذین اشتهروا أنّهم لا یحدثون إلا عن ثقات، وفی مرة یقول: لو لم أحدثکم إلا عن ثقة ما حدثتکم إلا عن ثلاثین، وفی روایة: ما حدثتکم إلا عن ثلاثة، فالتوثیق لا بد أن ینظر، ویسمى رجاله.  

And “Shu’ba bin al-Hajjaj” is amongst those who are known as guys who just quote narrative from reliable guys and he says: if I just wanted to quote narrative for you from reliable narrators, I’d quote narrative from thirty persons, and he says in another narrative: only from three persons. So, to make sure if that guy is reliable, we should search and their name must be said.

“Aal-Muqtarah fi Ajuba Ba’z Asa’lah al-Mustalah – p 57