Origin and history of saga

[proverb, saying, maxim], Middle English saue, at first in a general sense, "what is said, talk, words," from Old English sagu "saying, discourse, speech, study, tradition, tale," from Proto-Germanic *saga-, *sagon- (source also of Middle Low German, Middle Dutch sage, zage, German Sage "legend, fable, saga, myth, tradition," Old Norse saga "story, tale, saga"), from PIE root *sek(w)- "to say, utter" (see say (v.)).

The surviving specific sense of "proverb, saying, maxim" is by late 13c. "[A] contemptuous term for an expression that is more common than wise" [Century Dictionary].