Talmud (Rodkinson Edition) — Book 2…
“ The rabbis taught: Whoso vows to derive no benefit from his neighbor for a year, must reckon (for the year) twelve months, from day to day; but if he said "for this year," if he made the vow even on the 29th of Elul, as soon as the first of Tishri comes, that year is complete, for he vowed to afflict himself and that purpose (even in so brief a period) has been fulfilled. But perhaps we should say Nissan (should be regarded as the new year in such a case) ? Nay, in the matter of vows we follow the common practice among men (who generally regard Tishri as the New Year) . ”
