Musnad Ahmad 457:4

Yazid narrated to us, Ismail bin Abi Khalid and Muhammad bin Ubayd informed us, Ismail narrated to us, from Qais bin Abi Hazim, from Abu Mas’ud al-Ansari, who said: The Messenger of Allah, peace and blessings of Allah be upon him, gestured with his hand toward Yemen and said: "Faith is here." He said: "Verily, harshness and hardness of hearts are in the *faddadin* (the loud-voiced, clamorous ones), the owners of camels, where the horn of Satan rises, in Rabi’ah and Mudar." Muhammad said: "At the base of the camels' tails."