Every data source control (SqlDataSource, ObjectDataSource...) has
FilterExpression property.
To apply filter you need something like this:
string filteringExpression = string.Format("Date >= '{0}' AND Date <= '{1} 23:59:59'",dateFrom.ToString("yyyy-MM-dd"),dateUntill("yyyy-MM-dd"));
yourDataSource.FilterExpression = filteringExpression;
and to remove filter you must set FilterExpression of your data source control to null.
yourDataSource.FilterExpression = null;