Musnad Abu Ya'la al-Mawsili 115:123

Abu Khaythama narrated to us, Yahya narrated to us, from Abu 'Aruba, Qatada narrated to us, that Anas bin Malik narrated to them that the Messenger of Allah (ﷺ) ascended Mount Uhud, and Abu Bakr, Umar, and Uthman followed him. It shook beneath them, so he said: "Be firm, for upon you is a Prophet, a Truthful One (Siddiq), and two martyrs."