Regarding hanging the thief's hand around his neck, he said, "It is a sunnah. The Messenger of Allah ﷺ cut off a thief's hand and hung it around his neck."
أخبرنا سويد بن نصر قال أنبأنا عبد الله عن أبي بكر بن علي عن الحجاج عن مكحول عن ابن محيريز قال
عن تعليق يد السارق في عنقه قال سنة قطع رسول الله ﷺ يد سارق وعلق يده في عنقه
[Its chain of transmission is daif]Abu Dawud narrated it in the Hudud chapter, in the section on the thief whose hand is hung around his neck, hadith no. 4411, from the hadith of Hajjaj bin Artah, with this wording. It is also found in Al-Kubra, hadith no. 7475. Tirmidhi, at no. 1447, said it is hasan gharib. See also the following hadith.