Jami` at-Tirmidhi Book 17, Hadith 30
"I asked Fadalah bin 'Ubaid about hanging the hand around the neck of the thief: 'Is this from the Sunnah?' He said: 'A man came to the Messenger of Allah (ﷺ) with a thief so his hand was cut off, and then he ordered that it be hung around his neck.'"