The ornamental design for a handle for a sponge, as shown and described.
FIG. 1 is a left, front perspective view of my design for a handle for a sponge;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view of the handle for a sponge with environment.
The broken lines in the figures represent portions of the handle for a sponge as well as environment of the handle that form no part of the claimed design.