Deuteronomy 17:5-7

17:5 you must bring to your city gates that man or woman who has done this wicked thing – that very man or woman – and you must stone that person to death. 17:6 At the testimony of two or three witnesses they must be executed. They cannot be put to death on the testimony of only one witness. 17:7 The witnesses must be first to begin the execution, and then all the people are to join in afterward. In this way you will purge evil from among you.