When you wish to give advice to someone regarding any behaviour of his that you have come to know about, be gentle, talk to him in private and do not express explicitly what may be conveyed implicitly. Should he ask you to tell him who told you that which you know, do not tell him lest it stir up enmity. If he accepts your advice, praise God, and thank Him. If he should refuse, blame yourself.
Imam al-Haddad (The Book of Assistance)