Textbox validation to make sure has integer values only - asp.net

Question

Example textbox
Hi All, how can i add validate expression to only accept numeric and space in my textbox? Example as image above. I try this way ValidationExpression="[0-100' ']{100,}" but not correct..
<asp:TextBox ID="txtCopied" runat="server" TextMode="MultiLine"
Height="200px" Width="617px" />
<asp:RegularExpressionValidator ID="rvDigits" runat="server"
ControlToValidate="txtCopied" ErrorMessage="Enter numbers only till 100
digit" ValidationGroup="valGroup" ForeColor="Red" ValidationExpression="
[0-100' ']{100,}" />

Answer 1

<asp:RegularExpressionValidator ID="rvDigits" runat="server"
ControlToValidate="txtCopied"
ErrorMessage="Enter numbers only till 100
digit" ValidationGroup="valGroup" ForeColor="Red"
ValidationExpression="^[\d ]*$" />

Answer 2

I tried using ServerValidate instead of RegularExpressionValidator and tried to mess around with it.
<form id="form1" runat="server">
<asp:TextBox ID="txtCopied" runat="server" TextMode="MultiLine" Height="200px" Width="617px" MaxLength="2000" />
<asp:Button ID="Button1" runat="server" Text="Button" />
<asp:CustomValidator ID="CustomValidator1" runat="server" ControlToValidate="txtCopied" OnServerValidate="TextValidate"
ValidateEmptyText="True" SetFocusOnError="True" ErrorMessage="Enter numbers only till 100 digit" Display="Dynamic" />
</form>
Public Class WebForm1
Inherits System.Web.UI.Page
Protected Sub TextValidate(source As Object, args As ServerValidateEventArgs) Handles CustomValidator1.ServerValidate
Dim strRegex As String = "\b(0{0,2}[1-9]|0?[1-9][0-9]|1[1-9][0-9]|100)\b"
Dim re As New Regex(strRegex, RegexOptions.Multiline)
Dim ss As String() = args.Value.Split(" ")
For i = 0 To ss.Length - 1
args.IsValid = re.IsMatch(ss(i))
Next
End Sub
End Class