<asp:TextBox ID="TextBox1" runat="server" ValidationGroup="check"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="TextBox1" ErrorMessage="Lütfen sadece rakam girin" ValidationExpression="^\d+$" ValidationGroup="check">
</asp:RegularExpressionValidator>