Under the Indian law, a gift deed by itself is a legal instrument which is notarized and on a stamp paper. Why would one legal document need an affirmation through an affidavit (another legal instrument).
As per the Transfer of Property Act, 1882 (the law in India which governs transfer of movable and immovable property) in Chapter VII (which deals with Gifts) Section 123 clearly states:
123. Transfer how effected
For the purpose of making a gift of immovable property, the transfer must be effected by a registered instrument signed by or on behalf of the donor, and attested by at least two witnesses.
For the purpose of making a gift of movable property, the transfer may be effected either by a registered instrument signed as aforesaid or by delivery.
Such delivery may be made in the same way as goods sold may be delivered.
So in effect, there is no requirement for a written instrument. However, to show evidence of the gift to IRCC, a written instrument is required.
A gift deed or an affidavit is sufficient, as both, the stamp paper and the gift deed are executed on a Rs. 100 stamp paper, and the stamp paper is registered in the name of the person who is executing the document, i.e. the donor.
Further, section 122 defines a gift and lays down the requirement for how the gift is made:
122. "Gift" defined
"Gift" is the transfer of certain existing movable or immovable property made voluntarily and without consideration, by one person, called the donor, to another, called the donee, and accepted by or on behalf of the donee.
Acceptance when to be made-Such acceptance must be made during the lifetime of the donor and while he is still capable of giving.
If the donee dies before acceptance, the gift is void.
The basic requirements that you need to show in a gift deed are:
a. The transfer should be made voluntarily;
b. without consideration (no expectation of money or other favours); and
c . an acceptance by the donee.
The acceptance can be by signature, or by a physical transfer of funds, which happened in your case and you received the money. So if you have a place to sign on the gift deed, then just sign it, if there is no place for your to sign then you can just include the wire transfer details, or show the bank statement.