A written promise is a commitment or assurance made in writing by one party to another, promising to do something or refrain from doing something. Full definition
Despite all the earnest speeches, written promises in the Coalition agreement, and the PM's assurances that reform of lobbying was essential, once our careful and detailed report was published, the Government had gone cold and our report which should have been properly replied to within 3 months was ignored by the Government for over a year. (opendemocracy.net)
When I started writing A Promise of Fire over five years ago now, there was a good chance this manuscript would end up like my other works of fiction: perhaps unfinished, never seen by anyone but me, definitely never presented to agents or editors and using up space on my hard drive in a folder with a misleading enough name that hopefully no one would ever open it and stumble upon my first (and sometimes hilarious) attempts at writing a novel. (bookpage.com)
Hempt even obtained written promises from five of the country's leading trainers to race at his track. (si.com)