This is how the rendering equation is written in the textbook
$$L(p,\omega) = L_e(p,\omega) + \int f(p,\omega_i,\omega) \, L(p*,-\omega_i)\cos \theta \, d\omega_i$$
which component of this equation handles the shadowing?
Light that is blocked will mean that $L(p*, -w_i)$ under the integral is 0 plus how much light the blocking object itself reflects.
In other words the shadowing is embedded in the incoming light function.