Looking closely at the picture, there is corrosion on the hose at the lower right, a drop of water hanging from the upper hose, and more water hanging from the lower handle. It could be that the two supply lines are both leaking, the lower one more and for longer, rather than the valve has gone bad. Dry it all off thoroughly and put some bits of paper towel around and it will locate exactly where the water is coming from.
Or the valve could be bad, hard to determine these things from just a picture, and we were not told if it won't shut off all the way, was stuck open or closed, or had some other problem. Rather than replacing that valve, the OP might be able to repair it. There are probably rubber washers inside and some sort of packing under the packing nuts. The advantage of fixing it, rather than replacing it, is that there is little chance the pipe going into the wall will be damaged. The downside is that after taking it apart it may turn out to use some impossible to find bizarre washer, or the metal inside may be worn or corroded. In that case, it can still be replaced as was the original plan, but the water will need to be off for a while until a plumber can come.
