# how to prove B1 as a consistent estimator in panel data

$$Yi=a+ B_1*X_i+ B_2*Z_i+\epsilon_i$$, and suppose that $$Zi$$ is unobservable and not correlated with $$X_i$$. Is the OLS estimator of $$B_1$$ consistent by regressing $$Y_i$$ on a constant a and $$X_i$$?

I have no idea how to prove it.