This isn't an Islamic example, but during WW2 the prime minister of the UK Churchill had the British intelligence crack a german encrypted code. Once they broke the code they learned a bomb raid was due to start on the city of Coventry. They had to decide whether they should warn the civilians living in Coventry that bombs will fall from the sky into their heads, if they did warn them, it would let the Germans know they'd broken the code rendering any further intelligence useless, or they could not warn the civilians in Coventry about the attack which would cause the death of thousands of civilians but it would also keep the fact the code had been broken a secret, meaning they could go on to gather more intelligence. Churchill decided not to warn the civilians of Coventry and soon after thousands of people, all civilian, lost their lives, but the code was safe, the Germans didn't know it had been cracked and it was that code which eventually won the war.

Most people would argue Churchill did the right thing, although thousands died, it ultimately saved tens of thousands of lives by bringing WW2 to an end. That's not an Islamic example, it's just an interesting example to think about because rarely in war is anything such a black and white issue...