Musannaf Ibn Abi Shayba 33:182

Abu Khalid al-Ahmar narrated to us, from Bahz ibn Hakim, from his father, from his grandfather, who said: I said, "O Messenger of Allah, where do you command me [to go]?" He said, "Here," and he pointed with his hand toward al-Sham. "You will be gathered on foot and riding, and you will be gathered upon your faces."