大比丘三千威儀 2.101

2.101

從八月十六日至臘月十五日為一時，百二十日屬冬。從臘月十六日至四月十五日為一時，百二十日屬春。從四月十六日至八月十五日為一時，百二十日屬夏，為長歲盡。從八月十六日至臘月十五日即屬冬。作沙門不更夏，雖得鉢惒蘭不得歲。或有十五日得歲者，或十六日得歲者沙門。

From the sixteenth day of the eighth month to the fifteenth day of the twelfth month is one season; these one hundred and twenty days belong to winter. From the sixteenth day of the twelfth month to the fifteenth day of the fourth month is one season; these one hundred and twenty days belong to spring. From the sixteenth day of the fourth month to the fifteenth day of the eighth month is one season; these one hundred and twenty days belong to summer, marking the completion of the full vassa. From the sixteenth day of the eighth month to the fifteenth day of the twelfth month, it then belongs to winter. A śramaṇa who has not completed the summer retreat, though he may observe pravāraṇā, does not gain seniority in years. There are śramaṇas who gain their seniority on the fifteenth day, and there are śramaṇas who gain their seniority on the sixteenth day.