Now that you have defined a tooltip for the textbox,you can set the active property of the tooltip to false.
this
.toolTip1.Active = false;
then in the hover event,
Get the tooltip associated with the textbox as -
string toolTip = this.toolTip1.GetToolTip(this.textBox1);
//Set the value in the label
this.label1.Text = toolTip;
Hope this helps