  We study an irregular singularity of Poincar\'e rank 1 at the origin of a
certain third-order linear solvable homogeneous ODE. We perturb the equation by
introducing a small parameter $\varepsilon\in (\mathbb{R}_+, 0)\,(\varepsilon <
1)$ which causes the splitting of the irregular singularity into two finite
Fuchsian singularities. We show that when the solutions of the perturbed
equation contain logarithmic terms, the Stokes matrices of the initial equation
are limits of the part of the monodromy matrices around the finite resonant
Fuchsian singularities of the perturbed equation.
