He has already had a spat with Qais, with neither knowing the other's true identity. In the turn of events that follow, Qais's father dies at the hands of Tabrez. Qais in turn, avenges his father's murder by killing Tabrez.
A previous altercation between He and Qais remained hidden due to their unknown identities. Nevertheless, when Qais's father was assassinated by Tabrez, Qais sought revenge by slaying Tabrez in response.