Musnad Ahmad 30:314

Abu Mu'awiyah and Ya'la narrated to us, they said: Al-A'mash narrated to us, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The people of Yemen have come to you; they are the softest of hearts and the most tender of souls. Faith is Yemeni, and wisdom is Yemeni." Abu Mu'awiyah said, meaning in his hadith: "The head of disbelief is towards the East."