When someone deletes a WhatsApp message "for everyone", WhatsApp shows "This message was deleted". WhatsApp itself has no way to show it again. Notification History & Log (Notify Pro) can, because it saves the notification the moment the message arrives.

Set it up before the next message

Install the app and allow notification access.
Allow it to run in the background and turn off battery optimization, so saving never stops.
Make sure WhatsApp notifications are on and the chat is not muted.

Read a deleted message

Open the app and go to Deleted messages.
You see the deleted message with the sender, the time and pictures that were shown in the notification.
Turn on Deleted message alerts to get notified when a message is deleted.

Messages sent or deleted before you installed the app cannot be recovered by any app. Messages from muted chats, or from a chat you had open on screen, never create a notification, so they cannot be saved.

Is it safe?

Your notifications are stored only on your phone. The app does not upload or read your messages. You can protect the app with your fingerprint and delete everything at any time.

More details: How to Read Deleted Messages with Notify Pro.

Get Notification History & Log on Google Play