In Mundhum, there is a story of three brothers explaining the origin of major ethnic groups Mukubung was the eldest, Harkabung the middle and Riblabung the youngest were three brothers. The three brothers reached the Khuwalug rock and the path to the north was closed. Mukubung sacrificed a red-vented bulbul and offered its blood to the rock and passed through the rock. He migrated to the northern most part and Bhotiya people are said to be descended from him. Harkabung cut the pinky finger of a little girl, who was with him, and offered the blood and passed through the rock. He moved to the middle hilly region and Kirati people are said to be descended from him. His sons further migrated to various places of eastern Nepal and formed the various clans of Rai ethnic group. Riblabung, however could not offer anything to the rock and went south. He is considered the ancestor of the Tharu people of eastern Nepal.
