大比丘三千威儀 2.101

2.101

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.