Washing Cast Iron?

[meat killer 86]

My dad has a pot that was my great grandfathers. He let me use it when I was in high school to take to a friends house and cook. Brought it back clean and he immediately noticed something off. I thought it looked great. First thing he said was, " YOU WASH THIS WITH SOAP?"
Well duh yea I did.
Thought my dad was going to kill me. He said my great grandfather would be going nuts right now.
Dad said it was a huge no no to use soap.
Never made that mistake again.
That pot is so well seasoned it's like a nonstick pot. For the most part dad usually wipes it out and puts it back in the cabinet. If it's anything else it's hot water and a paper towel. Slowly heat back up and add a little oil and then cool then it's ready to go.