S. 54B : Capital gains-Land used for agricultural purposes-Mistakenly offered as taxable income-Assessing Officer accepted the return-Appeal filed before the CIT(A) on the ground that the income was shown mistaken belief that the same is taxable-CIT(A) dismissed the appeal-Held that dismissal of appeal is not justified-Article 265 of Constitution of India prohibits tax to be collected without authority of law.[S. 2(14)(iii), 139(1), 246A, 250, Art. 265]