Musannaf Ibn Abi Shayba 27:798

Yazid ibn Harun narrated to us, from Ibn Abi Dhi'b, from al-Harith ibn 'Abd al-Rahman, from the son of Jubayr ibn Mut'im, from his father, who said: We were with the Messenger of Allah, may Allah bless him and grant him peace, on a journey of his. He said, "There will emerge upon you the people of Yemen, as if they are the clouds; they are the best of those on the earth." A man from the Ansar said, "Are we not [the best], O Messenger of Allah?" He said a soft word: "Except for you."