Proof of Marriage

"First of all, very diligent care must be taken that the fact of a contracted marriage be shown by lawful proofs; if these proofs, although diligently sought, cannot be had, let an oath be tendered to the parties, by which they confirm their own assertion. When this has been furnished, let the parties be held as joined by lawful marriage, and their offspring as legitimate. Cases, however, are to be excepted in which the law requires full proof, for example if there is question of prejudice to another marriage or of receiving orders.

But a marriage confirmed by oath as above is to be entered not indeed in the common book of marriages, but in a distinct little book destined for this purpose." Sacred Congregation of the Sacraments, March 6, 1911.