Musnad Ahmad 903:11

Hashim ibn al-Qasim and Aswad ibn Amir narrated to us, they said: Sharik narrated to us, from ‘Asim, from ‘Abdullah ibn Sarjis, who said: "I saw the Prophet, may Allah bless him and grant him peace, and I entered upon him, and I ate of his food, and I drank of his drink. And I saw the Seal of Prophethood." Hashim said: "In the hollow of his left shoulder, as if it were a collection of black moles upon it, resembling warts."