It is not only the days of Purim that are days of rejoicing; rather, throughout the entire month of Adar, “the month that was transformed for them from sorrow to joy” (Esther 9:22), one should increase his rejoicing.

Rav Yehuda, son of Rav Shmuel bar Sheilat, said in the name of Rav: Just as when the month of Av begins one decreases his rejoicing, so too, when Adar begins, one increases his rejoicing…

Rav Pappa said: Therefore, in the case of a Jew who has litigation with a gentile, let him avoid it in Av, when his fortune is bad, and make himself available in Adar, when his fortune is good. (Ta’anit 29a)