The Mahdi will have the sign of our Prophet (saas) on his shoulder.
(al-Haythami, Al-Qawl al-Mukhtasar, p. 41)
The sign of the Prophet (saas) is on his shoulder.
(Barzanji, Al-Isha'ah, p. 165; Al-Muttaqi al-Hindi, Al-Burhan fi Alamat al-Mahdi, p. 23)
The mark of the Prophet (saas) is on his shoulder.
(Barzanji, Al-Isha'ah, p. 163)
As can be seen from these hadiths, the Mahdi will have "the sign of the Prophet (saas)," an evident mark, between his shoulders. Islamic sources describe this mark as follows:
Jabir ibn Samura narrates:
The seal of the Messenger of Allah (saas) was the size of a pigeon's egg. (Tirmidhi)
Abdullah ibn Sarjis narrates:
I saw the seal of the Prophet (saas) between his shoulder blades, the left part covered with freckles reminiscent of warts. (Ibn Kathir, Shamail Rasul, p. 53)
Abu Saib ibn Yazid relates that: "My eye saw the seal of the Prophet (saas) between his shoulders."
(Sunan Tirmidhi, 6:126)