That's not correct. Do you have any evidence where does Islam say so? The punishment of a criminal is what determined by the Sharia law. If someone has been found guilty of theft and the machines or the executer is not able to chop his hand off, it will be continued until the hand is separate from the arm. Same is the case with the hanging.....
same is not the case with hanging buddy. have u ever heard ke falanay ko 3 ya 4 martaba saza e maut ho gai. anywayz i dont have proof but this is something to search for.