let us see an authentic narration from musnad ahmad 

Anas narrates that a man was charged with adultery with a woman. Holy prophet asws sent hazrat ali asws to kill him. When hazrat ali asws met him, he was in a well taking coolness from that. Hazrat ali asws told him to hand over his hand to him. And he saw that he did not have the man’s sign/private organ at all. Hazrat ali asws came back and told holy prophet that he is man who does have man’s part at all.

[musnad ahmad, urdu, vol 5, page 857]

molvi zafar says sahih as per muslim

Sheikh shoaib says sahih on terms of muslim [21/405/13989]

Interesting, we see that holy prophet ordered to kill man,who was not even a man, just on the grounds of a charge
No witnesses, no proofs
he was really lucky that he was seen in the last time