I am about to be given a substantial gift. The donor has requested my social security number for taxes. Legit?

I have been offered a substantial monetary gift. The donor has requested my social security number so that he can report that the taxes has been paid off the top. He states that he is going to pay a flat percentage of taxes off the top of the gift, so that when I file my taxes this year, the IRS will know the taxes have already been paid and if there is any overpayment of taxes, that any refund will come to me directly. Is this necessary?