Capital gains exemption

Hi all,

As we all know that when new property is purchased for claiming capital gains exemption, the same should not be transferred within 3 years.

Can somebody please advise which date will be considered for computing the period of 3 years, will it be,

1. Date of making substantial payment for the property?

2. Date of Registration of the property?

3. Date of Possession of the property?

Please answer with relevant case law if possible...

urgent matter...

Thanks in advance...