One of those creatures wrote you once, ‘do not call up any that you can not put down’.
Notes from Wikiquote
"The Case of Charles Dexter Ward", written 1927, first published in Weird Tales, July 1941
Quote text and notes from Wikiquote: H. P. Lovecraft (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.