Motion blur due to camera shake is a annoying problem in low-light photography. In this paper, we propose a novel method to recover a sharp image from a pair of motion blurred and flash images, consecutively captured using a hand-held camera. We first introduce a robust flash gradient constraint by exploring the correlation between a sharp image and its corresponding flash image. Then we formulate our flash deblurring as solving a maximum-a-posteriori problem under the flash gradient constraint. We solve the problem by performing kernel estimation and non-blind deconvolution iteratively, leading to an accurate blur kernel and a reconstructed image with fine image details. Experiments on both synthetic and real images show the superiority of our method compared with existing methods.