The shear flow-aligned active nematic within a cuboidal channel is subjected to an external magnetic field (1.8T) in the aligned nematic direction. In the absence of the magnetic field, bend deformations proliferate, generating flows perpendicular to the initial alignment, as seen in the control case where no external field is applied (PIV vectors overlaid on the image for visual representation). Under the influence of the magnetic field, the bend instabilities are quelled, as there are no flows perpendicular to the applied field. Tracer beads are utilized for brightfield imaging in the magnetic field apparatus to distinguish between the conditions, while fluorescently labeled microtubules are observed in the control scenario.