From Longman Dictionary of Contemporary Englishwithout failwithout faila) ALWAYS/EVERY TIMEif you do something without fail, you always do it Tim visits his mother every day without fail. b) CERTAINLY/DEFINITELYused to tell someone very firmly that they must do something I want that work finished by tomorrow, without fail! → fail
Examples from the Corpus
without fail• You must take the medication every day without fail.• Danny comes over every Sunday without fail.• I want that work finished by tomorrow, without fail!• My mother goes to church every week without fail. 