use compare validator for this
example:-
<itemtemplate>
<ItemTemplate>
<asp:TextBox
id="txtDateOfPayment"
Text='<%# Bind("DateOfPayment") %>'
Runat="server" />
<asp:CompareValidator
id="cmpDate"
Text="(Invalid Date)"
ControlToValidate="txtDateOfPayment"
Type="Date"
Operator="DataTypeCheck"
Runat="server" />
</ItemTemplate>