A.T. Robertson Commentary 2 Corinthians 13:1

"This is the third time I am coming to you. At the mouth of two witnesses or three shall every word established." — 2 Corinthians 13:1 (ASV)

The third time I am coming (τριτον ερχομα). Either the third that he had planned to come or that he had been twice. The warning is made by quoting De 19:15.