Musnad Ahmad 510:1

Waki’ narrated to us, Qurrah ibn Khalid narrated to us, from Humayd ibn Hilal al-‘Adawi, from Khalid ibn ‘Umayr, a man from among them, who said: I heard ‘Utbah ibn Ghazwan saying: "I have seen myself as the seventh of seven with the Messenger of Allah, may Allah bless him and grant him peace, having no food except the leaves of the *hablah* (a type of desert tree), until the corners of our mouths became ulcerated."