  We present a comprehensive spectro-polarimetric study of persistent Black
hole X-ray binary 4U $1957\!+\!115$ with {\it IXPE} and {\it NICER}
observations. The source is observed in disk dominated thermal state with disk
temperature, kT$_{in}\approx1.4$ keV. The emission during thermal state from
the source is found to be moderately polarized and \textit{IXPE} measures a
degree of polarization (PD) $= 1.95\pm0.37\%$ ($>4.79\sigma$) along with a
polarization angle (PA) $= -42.78^{\circ}\pm5.41^{\circ}$ in the energy range
of $2-8$ keV. PD is found to be an increasing function of energy, whereas PA
indicates switching within the energy range which could be due to high
inclination and the returning radiation within the system. Simultaneous energy
spectra ($0.6-10$ keV) from {\it NICER} are modelled to study the spectral
properties. Furthermore, the spin parameter of the black hole is estimated with
spectro-polarimetric data as a$_{\ast}=0.988\pm0.001\,(1\sigma)$, which is
corroborated by {\it NICER} observations. Finally, we discuss the implications
of our findings.
