onclick event getting executed inspite when onclient click event returns false

Question

I have a validation function written in external JavaScript file.

I call this function using onclient property. It was running successfully until I added a stored procedure to insert data in database which gets called on the same button click.

Now my JavaScript function is not getting called and inconsistent data gets stored in database.

Code snippet:

    <asp:Button ID="Button1" runat="server" BackColor="#3333FF" ForeColor="White" 
     Text="Submit" Width="127px" OnClientClick="User_validation();"
     onclick="Button1_Click" />
&nbsp;</td>