Sheikh `Abdul-Majeed Subh, a prominent Azharite scholar, states: “When a Muslim witnesses an evil such as backbiting or the like they have to denounce this evil and to fear nothing but Allah. However, we advise to be gentle and kind when denouncing this evil. One should advise those committing sin in a wise way trying to attract them to accept their advice and to stop committing evil.
If we supposed that they did not stop this evil and you lost all hopes in reforming their behaviour after long experiences with them, one may pay their attention that their insistence on backbiting others may allow a Muslim to abandon such gatherings. Then, if after a period of time one has lost all hopes in changing their behavior, then we are permitted to forsake their gatherings and we are not obliged to visit them in such occasions.
May Allah guideus all to the right path, amen!”