On Yuan Chwang's Travels in India, 629–645 A.D. v1.c8.s3.7

v1.c8.s3.7

"Hence the professed Buddhists of India, complying with the sacred instructions of the Buddha, observe (lit. sit) two periods of Retreat, either the early or the later three months. The former period begins on our 16th day of the 5th month, and the latter on the 16th of the 6th month. Previous translators of the Sūtras and Vinaya use "Observe the summer" or "Observe the end of the winter". These mistranslations are due to the people of outlying lands not understanding the standard language, or to the non-harmonizing of provincialisms".