When the Philistines captured the ark of God, they brought it from Ebenezer to Ashdod;
then the Philistines took the ark of God and brought it into the house of Dagon and placed it beside Dagon.
When the people of Ashdod rose early the next day, there was Dagon, fallen on his face to the ground before the ark of the Lord. So they took Dagon and put him back in his place.
But when they rose early on the next morning, Dagon had fallen on his face to the ground before the ark of the Lord, and the head of Dagon and both his hands were lying cut off upon the threshold; only the trunk of Dagon was left to him.
References for 1 Samuel 5:4
This is why the priests of Dagon and all who enter the house of Dagon do not step on the threshold of Dagon in Ashdod to this day.