SB 10.44.10
na sabham praviset prajñah
sabhya-dosan anusmaran
abruvan vibruvann ajño
narah kilbisam asnute
Translation:
A wise person should not enter an assembly if he knows the participants there are committing acts of impropriety. And if, having entered such an assembly, he fails to speak the truth, speaks falsely or pleads ignorance, he will certainly incur sin.