Reply To: Commemorating Mosheh Rabbenu for Zayin Ador

Where is the inyan of there being an Adar A and Adar B first mentioned in Tanach or was it brought down later by chazal? My vague recollection is references to a chodesh by the number (aka 7th month) or in the context of other naarative where the time is known (aka h’chodesh hazeh lachem rosh chadashim). But where do we find the first reference to Tishrei , Adar Aleph etc.