οἱ δὲ εἶπαν· Ἐπέτρεψεν Μωϋσῆς βιβλίον ἀποστασίου γράψαι καὶ ἀπολῦσαι.
This answer of the Pharisees about Moses and divorce can also be found in Matthew, chapter 19:7, with some minor changes. The Pharisees are here responding to the question of Jesus, rather than the other way around, as in Matthew. Mark indicated that the Pharisees said (οἱ δὲ εἶπαν) that Moses allowed a man to write a certificate of divorce or dismissal (Ἐπέτρεψεν Μωϋσῆς βιβλίον ἀποστασίου γράψαι). Thus, the man could then divorce her or send her away (καὶ ἀπολῦσαι). The reference to Moses is from Deuteronomy, chapter 24:1-4, where there was talk about a certificate of divorce, and the possibility of many marriages. This certificate was called in Hebrew a “get.” Clearly divorce for a man was okay. However, after the second marriage there was a defilement.