Ex 12:2

12:2 The first month of the Hebrew year was Abib (March/April). This verse appears to report the institution of this new religious calendar, in commemoration of the Exodus. An autumn calendar is attested at 23:16; 34:22, though these passages may reflect an unofficial agricultural calendar. In the later Babylonian (spring) calendar the month of Abib is called Nisan (Neh. 2:1; Esth. 3:7).