You haven't thought this through properly, have you? What about when you want to put the wire back? and you have to knock the tiles off?
Isolate the cable.
"Power shower" is one with a pump that mixes hot and cold - there should be an FCU or a small switch somewhere. If its an FCU, take the fuse out and tape over the fuse holder. If just a switch, take the wire out of the output terminals on that (turning off the power whilst doing so).
If its, in fact, an electric shower, which heats the water itself, turn off the MCB, or pull the fuse. If you do have fuses or plug-in MCBs, take the fuse holder to the shower area, and tape it to the cable. If you just have normal MCBs, turn it off, and un-do the output wires from the back of the pull cord isolation switch.
Then tape over the end of the cable (each core seperate) where it hangs off the wall, so you can tile around it.