Musnad Ahmad 25:534

Ya'qub narrated to us, he said: My father narrated to us, from Ibn Ishaq, he said: Muhammad ibn Muslim al-Zuhri narrated to me, from 'Ubayd Allah ibn 'Abd Allah ibn 'Utbah, from 'Abd Allah ibn 'Abbas, he said: "Then the Messenger of Allah, may Allah bless him and grant him peace, proceeded on his journey and appointed Abu Ruhm Kulthum ibn Husayn ibn 'Utbah ibn Khalaf al-Ghifari as his deputy over Medina. He departed when ten days of Ramadan had passed. The Messenger of Allah, may Allah bless him and grant him peace, fasted, and the people fasted with him, until when he was at al-Kadid—a water source between 'Usfan and Amj—he broke his fast. Then he proceeded until he encamped at Marr al-Zahran with ten thousand of the Muslims."