Musnad Abu Ya'la al-Mawsili 115:331

Abu Musa narrated to us, Yahya bin Sa'id narrated to us, from Sa'id, from Qatadah, that Anas bin Malik narrated to them: That the Prophet of Allah (may Allah bless him and grant him peace) ascended Mount Uhud, and Abu Bakr, Umar, and Uthman followed him. It shook with them, so he said: "Be still, for upon you is a Prophet, a truthful one (Siddiq), and two martyrs."