You can create Back-up of your messages in Whatsapp.
For this follow this→open Whatsapp→Settings→Chat Settings→select Backup Conversation.
This will create backup of your messages in Whatsapp folder(Whatsapp→Databases→msgstore.db.crypt7) found in internal storage of phone.
To restore the Back-up messages, you will need to uninstall and reinstall WhatsApp. During the installation process, you will be prompted to restore your message history. Choose Restore to restore your missing chats.