Follow the Steps -:
1) Go to file manager then SD card and then go to Whatsapp database folder.
2) Here you can see some file names in the format: msgstore-yyyy-mm-dd.1.db.crypt.
3) Similarly, you can also observe a file named as msgstore.db.crypt (rename this file by adding anything before or after it).
4) After renaming it, select the file with date that consist of message that you have deleted accidently.
5) Now rename the selected file to msgstore.db.crypt.
6) Finally, go to settings then application then to manage application and then go to Whatsapp and click on clear data.
7) Now run your Whatsapp and select restore and your file saved as msgstore.db.crypt will be restored.