A.T. Robertson Commentary Matthew 26:72

"And again he denied with an oath, I know not the man." — Matthew 26:72 (ASV)

With an oath (μετα ορκου). This time Peter added an oath, probably a former habit so common to the Jews at that time, and denied acquaintance with Jesus. He even refers to Jesus as "the man" (τον ανθρωπον), an expression that could convey contempt, "the fellow."