Three ways to stop someone commenting SIN.

The Prophet Muhammad (peace be upon him) said: 

"If you see anybody commenting sin.

1. You must stop him with your hands.

2. If you do not have power to stop with your hands, so stop you must stop him with your tongue.

3. If you do not have power to stop with your tongue, so you must stop him from your heart.

This is the weakest Faith."