Asalha Puja (known as Asanha Puja in Thailand) is a Theravada Buddhist festival which typically takes place in July, on the fifteenth day of the waxing moon of the eighth lunar month. It commemorates the Buddha’s first sermon in the Deer Park in Benares and the founding of the Buddhist Sangha. In Thailand, Asalha Puja is a government holiday.
The day is observed by donating offerings to temples and listening to sermons. The following day is known in Thailand as Wan Kao Pansa; it is the first day of vassa, the Theravada rains retreat.