OSPF Filtering

I am looking to stop a routeros from redistributing 10.0.0.0/8 to the rest of the OSPF network. How can I do this.

I tried the folloging with routeing-test package but no luck so far:
0 chain=ospf-in prefix=10.0.0.0/8 action=!accept

1 chain=ospf-out prefix=10.0.0.0/8 prefix-length=8 action=discard

2 chain=ospf-out action=reject


In line 0 I have tried all potential actions.
A my missing something?

thanks
Carlo