You need to use OnClick event to redirect from one page to another.
protected void Redirect(object sender, EventArgs e)
{
Session["TextBox"] = this.txtTextBox.Text.Trim();
Response.Redirect("~/Page.aspx");
}
And when you came back to same page check the content of Session.
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
if (!this.IsPostBack)
{
if (Session["TextBox"] !=null)
{
this.txtTextBox.Text = Session["TextBox"].ToString();
}
}
}
}