A proof of execution is the one notarial act in which the person whose signature is being certified never appears, and California compensates for that absence with an unusually strict identification requirement for the person who does appear. The subscribing witness must be identified by a credible witness who is personally known to the notary — not by a driver's license, not by a passport, and not by any number of documents. The reasoning follows from the structure: the whole act rests on the subscribing witness's word, so the state requires that someone the notary already knows personally vouch for who that witness is. Documentary identification, adequate for an ordinary acknowledgment where the principal appears, is not adequate here. There is no substitute and no workaround: producing a passport does not satisfy it, two people vouching does not substitute for one credible witness personally known to the notary, and journaling the difficulty does not excuse it. Without that credible witness, the proof cannot proceed.