BT BB 29a(15) :שתא קמיתא מזדהר איניש בשטריה תרי מזדהר תלת נמי מזדהר טפי לא מזדהר‏ : a man guards his deeds the first year, guards them the second (year, and) guards them also the third (year). He does not guard (them) more
See the entire entry for zhr vb. to beware