Article 5 of the Constitution of India: Citizenship at the commencement of the Constitution.

5. Citizenship at the commencement of the Constitution.—

At the commencement of this Constitution, every person who has his domicile in the territory of India and—
(a) who was born in the territory of India; or
(b) either of whose parents was born in the territory of India; or
(c) who has been ordinarily resident in the territory of India for not less than five years immediately preceding such commencement,
shall be a citizen of India.