G4526 — sakkos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
sakkos — pronounced sak'-kos
of Hebrew origin (8242); "sack"-cloth, i.e. mohair (the material or garments made of it, worn as a sign of grief):-- sackcloth. see HEBREW for 08242
4 occurrences in the KJV.
Matthew 11:21
Woe unto thee, Chorazin! woe unto thee, Bethsaida! for if the mighty works, which were done in you, had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes.
Luke 10:13
Woe unto thee, Chorazin! woe unto thee, Bethsaida! for if the mighty works had been done in Tyre and Sidon, which have been done in you, they had a great while ago repented, sitting in sackcloth and ashes.
Revelation 6:12
And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood;
Revelation 11:3
And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.