I want to write a check against my business line of credit and deposit it into my business checking (operating) account.

I use Quick Books. I do not want to record this transaction as income or sales, so what is the correct entry? I know I have to debit "cash", my business checking account, but what account do I credit?

Getting money from a line of credit is a loan and you owe it back to the bank. So it's a liability. If it were me, I'd want to create a separate liability account just for the line of credit to keep it separated.