Rails - Jun 2009 - Prompt option not available in rails date helper

Hi prompt option is not available in rails 2.2.but in api.rubyonrails it
hazs mentioned it is there.But its not working.

date_select("post", "written_on",
:prompt=>{:day=>''Select day'',
:month=>''Select month'', :year=>''Select
year''})

Please give some idea
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