Here is step by step guide as how to see deleted messages from whatsapp:
Step 1: Enter the notification log manually.
Step 2: Long press on your home screen and select widgets.
Step 3: Scroll until you find settings widget.
Step 4: Pull that on your home screen.
Step 5: A new option will open with various options to choose from
Step 6: Select Notification log.
Step 7: From now on, this setting widget will directly lead you to your notification history.
Step 8: After the notification log is opened, you can see all your notification there.
Also you need to keep in perspective that you need to follow above steps in order and if you miss any steps you have to start all over again. Try it few times and you will get it right eventually. Also beware that opening a notification here will load all the intricate details of that particular notification, not just the text.
There is another method to see deleted messages from whatsapp. First, one can install Notification History application from Google Play Store, if you are using the Android phone. For Apple phones, its little bit tricky but you can still find the similar app in Apple store. After installing it successfully open the app and look for WhatsApp icon and you will be able to see those messages.
I also noticed that after restoring the deleted messages, only about first 100 characters of the message were visible. You can only retrieve messages from the last previous hours and not longer than that. Also only text can be restored and not any video or photo.