Farida Khan aka Sher Shah Suri met with Badal Singh, an Ujjaniya Parmar Rajput in the jungles of Bhojpur and became friends since both were victim of their stepmother plot. Later, Sher Shah helped Badal's son, Gajpati in getting his estate back and then Gajpati helped Sher Shah in defeating Humayun.

That's how Sher Shah Suri got the support of Ujjaniya Parmar Rajputs in Bihar. Source: Veer Kuer Singh by Lt. Gen. Sk Sinha.