20 CFR 219.31: Evidence of a valid ceremonial marriage.

(a) Preferred evidence. Preferred evidence of a ceremonial marriage is—

(1) A copy of the public record of the marriage, certified by the custodian of the record or by a Board employee;

(2) A copy of a church record of the marriage certified by the custodian of the record or by a Board employee; or

(3) The original certificate of marriage.

(b) Other evidence of a ceremonial marriage. If preferred evidence of a ceremonial marriage cannot be obtained, the applicant must state the reason therefor in writing and submit either—

(1) A sworn statement of the clergyman or official who performed the marriage ceremony; or

(2) Other convincing evidence, such as the sworn statements of at least two persons who have direct knowledge of the marriage, preferably eyewitnesses to the marriage ceremony.