  We consider the planar Ising model in rectangle $(\Omega; x^L, x^R, y^R,
y^L)$ with alternating boundary condition: $\ominus$ along $(x^Lx^R)$ and
$(y^Ry^L)$, $\xi^R\in\{\oplus, \text{free}\}$ along $(x^Ry^R)$, and
$\xi^L\in\{\oplus, \text{free}\}$ along $(y^Lx^L)$. We prove that the interface
of critical Ising model with these boundary conditions converges to the
so-called hypergeometric SLE$_3$. The method developed in this paper does not
require constructing new holomorphic observable and the input is the
convergence of the interface with Dobrushin boundary condition. This method
could be applied to other lattice models, for instance Loop-Erased Random Walk
and level lines of discrete Gaussian Free Field.
