It has been discussed in other topic/thread that Maghapuja celebration is reference from the commentary of MN 74 Dighanakkha Sutta (and the famous Ovada Pattimokha verses is found in Dhammapada and Mahapadana Sutta of DN)
Off course, the well-known celebration is evidently only observed in Theravada tradition. But I’m curious if there any reference of the event (gathering of 1250 Arahants without any invitation in which the Buddha preached Ovada Patimokkha) in northern Buddhist sources (in Chinese, Sanskrit, or Tibetan texts, etc.)?
I don’t think this story exists in the Chinese language sources at all? I just did a Google for terms 教授波羅提木叉 (ovada patimokkha) and 一千二百五十位大阿羅漢 (1250 great arahants) Several major Chinese Mahayana sutras, like the Diamond Sutra and the Buddha speaks the Amitabha Sutra, have references to 1250 arahants. But no hits for the Magha Puja story.
For a fairly detailed look at Chinese language sources on the ovada patimokkha, I found this article by Ven. Yinshun. http://www.shengyimaster.org/yinshun/33/yinshun33-06.html and this by Zhuang Chunjiang 印度佛教思想史要略, which are interesting if you read Chinese, but not a match for the story.
