How to set Additional Comments field mandatory to fill, whenever incident moved to canceled state.

[HrishabhKumar]

I have the following requirement:

Whenever an incident is moved to cancelled state, Additional Comments [comments] field should be mandatory to fill.

Let me know how it could be done, Thanks.

[Ankur Bawiskar]

@HrishabhKumar 

for your below requirement why won't before update BR won't help?

Whenever an incident is moved to cancelled state, Additional Comments [comments] field should be mandatory to fill.

If my response helped please mark it correct and close the thread so that it benefits future readers.