Ibnul Mubaarak (rahimahullaah) said: There is no harm in Al-Mu-allaa Ibn Hilaal (rahimahullaah) as long as he does not narrate hadeeth.  So a man from the soofiyyah said to him: O father of Abdur-Rahmaan! You backbite the righteous people? So he (Ibnul Mubaarak) became angry and said: Shut up, if we do not clarify the truth, then who will clarify it

He (rahimahullaah) said:

”Whoever is stingy with knowledge is put to trial with three: [1]Either with death, so his knowledge goes away; [2]Or forgetfulness; [3]Or put to trial by the ruler.

[Chapter: A mention of those who followed the followers of the companions: Source: Seeratus Salaf As-Saaleh by: Imaam Ismaaeel Bin Muhammad Bin Fadl Al-Asbahaanee (535AH)]