The Sun: Deleted WhatsApp messages can be restored from chat backups 
WhatsApp messages continue to be stored in the phone memory even after they are deleted from personal correspondence and group chats. As The Sun found out, they can be read using the backup function.
To recover deleted messages, you need to uninstall WhatsApp and then reinstall it from the app store. After logging in, the user will be prompted to use the messenger's backup copies existing on the device. After recovery, the messages will also contain deleted messages.
The Sun notes that the found method is far from the only one. You can also read deleted messages on WhatsApp using the notification log stored on the device. However, this requires the user to interact with the message notification, which was then removed. Also, restarting your phone can reset the notification registry.
Chats and all messages in WhatsApp are backed up by default at 2 a.m. local time every day. However, in the settings, you can change the frequency to weekly or even monthly.