A.T. Robertson Commentary Matthew 5:31

"It was said also, Whosoever shall put away his wife, let him give her a writing of divorcement:" — Matthew 5:31 (ASV)

A writing of divorcement (αποστασιον), "a divorce certificate" (Moffatt), "a written notice of divorce" (Weymouth). The Greek is an abbreviation of βιβλιον αποστασιου . Vulgate has here libellum repudii. The papyri use συγγραφη αποστασιου in commercial transactions as "a bond of release" (see Moulton and Milligan's Vocabulary, etc.) The written notice (βιβλιον) was a protection to the wife against an angry whim of the husband who might send her away with no paper to show for it.