Musannaf Ibn Abi Shayba 34:122

Ibn Bishr narrated to us, Mis'ar narrated to us, from 'Abd al-Malik ibn Maysarah, from Mus'ab ibn Sa'd, from Ka'b, who said: "The first person to take hold of the ring of the door of Paradise, so that it is opened for him, is Muhammad, may Allah bless him and grant him peace."