Magha Puja is an important religious festival celebrated by Buddhists on the full moon day of the third lunar Month for more than 2,600 years. It marks the four auspicious occasions in the Buddha time as follows: 1. It was the full-moon day of the third lunar month, 2. There were 1,250 Arahants, the enlightened disciple monks, who came to see Lord Buddha without any prior arrangement, 3. All of them were ordained by Lord Buddha, and 4. Lord Buddha delivered a sermon called the “Ovada Patimokkha” which includes the fundamental ideology, the moral standards and the conducts of Buddhism.
Sourced from https://www.maghapuja.org