Musnad Ahmad 126:2

Rawh narrated to us, Qurrah ibn Khalid narrated to us, he said: I heard Mu’awiyah ibn Qurrah narrating from his father, he said: I came to the Messenger of Allah, may Allah bless him and grant him peace, and I asked his permission to put my hand into his shirt collar, and he was praying for me. Nothing prevented me from touching him except that he was praying for me. He said: "And I found upon the protrusion of his shoulder something like a lump."