Joint collobaration agreement(whether business income or capital gain income)

Hello All, My Client is having inherited Land, on which he entered an agreeement with Developer that according to the agreement the entire development was to be done by the develop and the land owner was entitled to 55% of sales Consideration AND 45% will belong to developer. Now there are 25 Flats develop on that land. out of these 2 were sold, now the land owner has disclosed sales consideration(55%) and files his return and shown this income as Capital Gain income. Income tax department want to treat this as Business Income. Kindly suggest whether this is business income or Capital Gain Income. Please provide any case laws regarding this. (Very Urgent) Thanks in Advance