大宋僧史略 1.21

1.21

又䓗嶺北諸國。或以建未月為正首。或春際為夏安居。是知隨方宗計各別。況佛在西域說經。羅漢居竺乾造論。必不指東震之月。所言四月八日者。西域四月八日也。以事符合周書異記昭王四月八日祥瑞。疑翻譯時隨聲筆受。妄認夏正也。唯為有七月十五日。臘法經是用此方為文。令人惑之。故兩存也。

Furthermore, among the countries north of the Congling Mountains, some take the month pointing to wei as the start of the year, or take springtime as the summer retreat (varṣā). From this we know that principles and reckonings vary from place to place. How much more so when the Buddha preached the sūtras in the Western Regions and the arhats composed the treatises in India—they certainly did not refer to the months of the Eastern Land! What is called the eighth day of the fourth month is the eighth day of the fourth month in the Western Regions. Because this event corresponded to the auspicious omens on the eighth day of the fourth month under King Zhao in the Zhoushu yiji, I suspect that at the time of translation they took down what was spoken phonetically and mistakenly identified it with the Xia calendar. Only because there is the fifteenth day of the seventh month, where the Vinaya text on the end of the retreat used this land's calendar, people were confused by it; therefore both are preserved.