Sayyiduna Qurrah bin Iyas (may Allah be pleased with him) said: I came to the Messenger of Allah (peace and blessings be upon him) and put my hand inside his (peace and blessings be upon him) collar. He (peace and blessings be upon him) did not stop supplicating for me while I was touching the Seal of Prophethood. I saw the Seal of Prophethood on his (peace and blessings be upon him) shoulders, like a lump (a raised swelling).
Hadith Referenceالمعجم الكبير للطبراني / باب القاف / 16100