'Fasting' in the Bible

And in every province, whithersoever the king's commandment and his decree came, there was great mourning among the Jews, and fasting, and weeping, and wailing; and many lay in sackcloth and ashes.

in order to confirm these days of Purim at their proper time just as Mordecai the Jew and Queen Esther had established them and just as they had committed themselves and their descendants to the practices of fasting and lamentation.