According to Hindu mythology,
the Kumhars are the descendants of Lord Prajapati Daksha, son of Lord Brahma. Thats why Kumhars are are also known as Prajapati. One of Daksha Prajapati Daughter, Sati, was first wife of God Shiva.
Daksha Prajapati was a great scholar of Yajur Veda. Brahma give a prestigious rank to Daksha Prajapati, Then he perform a great yagna. He invited rishis, munis, devas and Brahmins to the yagna. On his arrival to the yagna mandap, all of these stood up in respect, except Brahma and Shankar. rajapati became angry at the apparent disrespect and declared that Shankar will not be allowed to take part in the Yagna. Shankar’s gate keeper, Nandi cursed all Brahmins that were there that their entire lineage will live in pity of others and will eat what others will give and will also be Demon-Brahmins. and hence many infants of Brahmins will become malicious in kaliyuga. But Kumhars were even then called Prajapatis and so there is no such curse given to this holy honest hardworking high system called Kumhar.Daksha also seem to be given same curse but Shiv purana tells that all Sons of Daksha were told Muki Marga and they become Mukta. This story of kumhars to be infants of only Prajapati Daksha seem to be false. But because prajapatis have surnames such as attris/bhardwaj/gautam/dhadhich etc., so they may be infants who did not study Vedas but worked hard so, those who studied Vedas, become Brahmins and who worked hard become Kumhars.