Pass this on
Most people arrive here because someone who cared passed it on. Pick a framing, change the words if you like, and send it yourself from your own phone or email. We never send anything, we don't know who you are, and the link never expires, because they may not be able to look for weeks, and that's fine.
If you're worried about someone
Say what you've noticed, not what you've concluded. "You seem to be walking on eggshells lately" lands better than "I think they're abusive." Don't criticise their partner; they'll defend them, and then they'll stop telling you things. Keep the door open: "I'm here whenever, no questions." Don't push them to leave. Leaving is the most dangerous time, and the decision has to be theirs.
If you think they're in immediate danger, call 999. For advice on how to help, the National Domestic Abuse Helpline (0808 2000 247) talks to friends and family too.