I need a regular expression that only accepts text characters with spaces allowed

Try this, for regular expression

^[a-zA-Z ]*$

You can add the RegEx character \s to your regular expression, allowing spaces, whitespace and line breaks:

^[a-zA-Z\s]*$

Or, like the other posters said, use a space, to only allow spaces:

^[a-zA-Z ]*$

Just add a space between the brackets.

^[a-zA-Z ]*$