Dear Student,
Hybridization is a concept based on the idea that the orbitals having a particular principal quantum number fuse together to form hybrid orbitals through which bonding takes place.
Since s-orbital is the first orbital for a shell having a particular principal quantum number, it is always a part of hybrid orbitals if hybridisation takes place , because electrons get filled first in the s orbital as it has the lowest energy for a particular shell.
Thus, hybridisation will always involve s-orbitals to form hybrid orbitals.
Regards