Naseehah is to be given in secret

Naseehah is most likely to bear its fruit when given to a person when he is by himself, for in such a situation the person is less likely to be affected by the thoughts of others. The sincere advisor should not aid the Devil over his brother by publicly rebuking him and letting Shaitaan beguile his brother into not taking the naseehah. This closes the doors of goodness and acceptance, and reduces the chances of the naseehah from being accepted.
This is why our pious predecessors used to give naseehah in secret. Hafidh Ibn Rajab writes, "When the righteous predecessors intended to give naseehah to someone, they admonished him privately, to the point that some of them said, "The one who exhorts his brother between him and himself , then it is naseehah. The one who exhorts him in front of people, then it is merely scolding!"
Fudail Ibn Ayyadh, one of the pious scholars from our predecessors, said, "A believer covers up and gives naseehah, whereas an evildoer exposes and humiliates." Ibn Rajab commented on Fudail's saying, "It is naseehah if it is with a cover, while humiliating is with broadcasting."