I recently noticed a water stain on the ceiling below the master bedroom shower. After scraping away the grout between in the space between the shower floor times and the shower wall times, I noticed a small hole. How and with what should I fill the hole before regrouting? The hole is about 2 inches long and 1/4 inch wide.

So you are saying the small hole is in the wood floor below the tile, right? Probably just file it with a little extra grout. There are many other reasons for a leaky shower other than cracked grout. Are you sure that this was the problem?

It seemed to be the most obvious place where water could escape. I will check the drain as well. Otherwise I will need to rip up the shower floor.