Musannaf Ibn Abi Shayba 37:313

Waki’ narrated to us, from Malik ibn Mighwal, he said: Musa ibn Qays narrated to us, from Salamah ibn Kuhayl, from Zayd ibn Wahb, who said: When we returned from Nahrawan, Ali said: "We have witnessed people in Yemen." We said: "O Commander of the Faithful, how is that?" He said: "By desire."