What did Mordecai put on when he learned of Haman's decree against the Jews?

Answer: Sackcloth and ashes

Mordecai tore his clothes, put on sackcloth and ashes, and went out into the city wailing loudly and bitterly.

“When Mordecai learned of all that had happened, he tore his clothes, put on sackcloth and ashes, and went out into the middle of the city, wailing loudly and bitterly.”— Esther 4:1 (BSB)