Abba Poemen: If I see my brother sin, is it right to say nothing about it?

A brother asked Abba Poemen:
"If I see my brother sin, is it right to say nothing about it?" 

The old man replied:
"Whenever we cover our brother's sin, God will cover ours; whenever we tell people about our brother's guilt, God will do the same about ours."

Abba Poemen