How To Put Comma In Value (1000)

I have a textbox named txtWith (Amount where cash should be inputted) and I want the input to have comma. Example, if I input 1000, I want it to be like this 1,000. By the way, this is my code in the textbox.

///THIS CODE WILL DISABLE CHARACTER///
Private Sub txtWith_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtWith.KeyPress
'////////////////LETTERS DISABLED ONLY///////////////////////
If (Asc(e.KeyChar) >= 48 And Asc(e.KeyChar) <= 57) Or Asc(e.KeyChar) = 8 Then
e.Handled = False
Else
e.Handled = True
MsgBox("Please input numbers only!", vbCritical, "Error!")
End If
End Sub