C. F. Keil and Franz Delitzsch on Nehemiah 9:1

Neh 9:1

On the twenty-second of Tishri was the Hazereth of the feast of tabernacles; on the twenty-fourth the congregation re-assembled in the temple, “with fasting and with sackcloths (penitential garments made of hair; see rem. Joe 1:8) and earth upon them,” i.e., spread upon their heads (1Sa 4:12; 2Sa 1:2; Job 2:12), - the external marks of deep mourning and heaviness of heart.