Origin of Kanyakubja Brahmins
There was the a son of Lord Brahma called KUSH. Kush had four sons named as KUSHABH, KUSHNABH, ASHRUTRAJAS and VASU. Kushnabh had one hundred extremely beautiful daughters through Ghritachee, an Apsara. The god of Vaayu (Air) was very much attracted by the beauty of these fair ladies & wanted to marry with them. These virgins told god Vaayu that they were the daughters of a rishi and they would marry with only that person as advised by their father and humbly denied the proposal of god Vaayu to marry with him. The god Vaayu was annoyed and cursed all these beautiful virgin daughters of Kushnabh become Hunchbacked or to become Kubja. These virgin hunchback daughters of Kushnabh were married with Brahma Dutta, the noble king of Kampilya, son of Choolie Rishi and Somada Gandharvee. As soon as, these virgin daughters of Kushnabh were touched by noble King Brahma Dutta, all these virgins were free from curse of god Vaayu. They became normal, their bumps were vanished and they regained their original beauty and charm.
Kampilya the kingdom of Brahmdutt later became famous by name of KANYAKUBJA (because he married the kubja daughters of Kushnabh). Now a day it is known as KANNAUJ. The native Brahmins of this land were later known as KANYAKUBJA Brahmins.
Reference from Valmiki Ramayan Balkand, Sarg 31-34: 1 2 3 4 5