How will that work? Hijri Calendar Supports max 29 days in .Net. Your date itself is wrong.
See this below. How you must work with Hijri Dates.
protected void Page_Load(object sender, EventArgs e)
{
System.Globalization.HijriCalendar hijri = new HijriCalendar();
string date = "1396-02-29";
DateTime hijriDate = new DateTime(int.Parse(date.Split('-')[0]), int.Parse(date.Split('-')[1]), int.Parse(date.Split('-')[2]), hijri);
}