Article 6 of CoI : Article 6: Rights of citizenship of certain persons who have migrated to India from Pakistan.

Explanation using Example

Example 1:

Ravi's grandfather was born in Lahore, which was part of undivided India before 1947. After the partition, Ravi's family migrated to Delhi in June 1948. Since Ravi's grandfather was born in India as defined in the Government of India Act, 1935, and the family migrated before July 19, 1948, and has been living in India since then, Ravi is deemed to be a citizen of India at the commencement of the Constitution.

Example 2:

Ayesha's parents were born in Karachi, which was part of undivided India before 1947. Ayesha's family migrated to Mumbai in August 1948. Ayesha applied for Indian citizenship before the commencement of the Constitution and was registered as a citizen by an officer appointed by the Government of the Dominion of India. Since Ayesha's parents were born in India as defined in the Government of India Act, 1935, and she has been a resident in India for at least six months before her application, Ayesha is deemed to be a citizen of India at the commencement of the Constitution.