The Constitution of the United States of America.
Amendment XV:
1. The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude.
2. The Congress shall have power to enforce this article by appropriate legislation.
and Amendment XIX:
The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of sex.
Congress shall have power to enforce this article by appropriate legislation.
that does not say anything about proving who you are