in writing
In a printed, written, or typed document. It's right there in writing that employees caught taking office supplies will be fired immediately. Please send me an email summarizing this conversation, so I have it all in writing should the issue come up in the future.
*in writing
in written form rather that spoken. (*Typically: get something ~; have something ~; put something ~.) Be sure to get their salary offer in writing.
in ˈwriting
in the form of a letter, document, etc. (that gives proof of something): All telephone reservations must be confirmed in writing.You should get his promises in writing.