ANSWER:

If you can present four male witnesses testifying that they had seen his private part in that woman’s private part, you can do that! Otherwise, you would be flogged 80 lashes for slandering him. You must mind your own business. 

sheikh, ive come to know that my neighbour who is married committed zina when his wife was nt at home.. what should i do now as am aware of it now.. should i conceal the fault because allah loves concealing sins or should i inform his parents or wife as to make him stop the guilt? Am very confused help me