How in CAML Query should I exchange e.Day.Date.ToLocalTime() by the Textbox.Text with date string

Question

how can I exchange e.Day.Date.ToLocalTime() by the Textbox.Text value.

I have this code:

                    string FullQuery = "<Where><And><Eq><FieldRef Name='{0}' /><Value Type='DateTime'>{1}</Value></Eq><Eq><FieldRef Name='Pracownik' /><Value Type='Text'>{2}</Value></Eq></And></Where>";
                string dateISO = SPUtility.CreateISO8601DateTimeFromSystemDateTime(Convert.ToDateTime(TextBox4.Text).ToLocalTime());
                var query1 = new SPQuery();
                query1.Query = String.Format(FullQuery, Convert.ToDateTime(TextBox4.Text).ToLocalTime(), dateISO, DropDownList1.SelectedItem.Text);
                query1.ViewFields = "<FieldRef Name='Kontrakt' /><FieldRef Name='Procenty' />";
                query1.ViewFieldsOnly = true;

                SPListItemCollection listaDniPrzeznaczonychNaProjekt = witryna.Lists["Szczegoly"].GetItems(query1);

                foreach (SPListItem olistaDniProjektowych in listaDniPrzeznaczonychNaProjekt)
                {
                    Label4.Text += olistaDniProjektowych["Kontrakt"].ToString();
                }

And I want to put there Textbox.Text

The debuger says me that the same of filds are incorect.