禍(わざわ)いも福(さいわい)の端となる。 There is no ill but may turn to one's good. The darkest hour is that before the dawn. It is always darkest just before the day downs.
禍いも三年たてば用に立つ。 Lay things by, they may come to use.
禍いを転じて福となす。 He that stumbles and falls not mends his pace.