From Data choose Validation.
The Allow box in the Settings tab does not include criteria for validating text.
You can validate a text entry, but you cannot check whether the entry is text or not.
Solution: Enter a formula that will check whether the data is text.

1. Choose Data, Validation.
   
2. Select the Settings tab.
   
3. In the Allow box, select Custom.
   
4. In the Formula box, enter =IsText(D4) (D4 is the first cell in the range).
   
5. Click OK.