I believe someone already responded to your ques.
In my opinion, it is easier to declare it as a gift rather than the other. You might confuse officer with the legal letter option. Why go to such extent when you have tested easier approach ?
If you decided to go with gift deed option, this template can be useful
GIFT DEED
I, Your Father Name, S/o Your Grandfather Name , R/o ADDRESS, do hereby on dated 00/10/2016 make a gift-deed for a gift made on dated of 00/10/2016, Rs. 000000/-
(Rupees Only) out of love and affection to my Son (Your Name), S/o Father Name, ADDRESS. I confirm that I am a resident of India. I, further confirm that this gift is
being made out of my own funds standing to the credit of my A/c No.- 000000000 in ABC Bank, Bank Address. I, further confirm that the consideration for this gift is
the love and affection for my Son (Your Name) and no other consideration.
I further confirm that the gift has been made by Cheque No. 000000 dated 00/10/2016 drawn on ABC Bank, BANK ADDRESS. This gift is irrevocable and I have no claim left
whatsoever on the said gifted amount and he is free to utilise it in any manner.
PLACE:
DATED:
(Your Father Name)
Witness:
The gift as stated above is accepted