Don't speak without knowledge and don't take knowledge from person who is not trustworthy

 Al-Qaasim bin Muhammad:

*❝The ugliest form of ignorance is that I speak without knowledge or I narrate from someone who is not trustworthy.❞*

[At-Tamheed, (1/39) 

Translated By Abū Ruqayyah 'Abd us-Samad]