Musnad Ahmad 30:3197

Isma'il narrated to us, he said: Hisham ibn Hassan informed us, from Ibn Sirin, from Abu Hurayrah, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The people of Yemen have come; they are the softest of hearts. Faith is Yemeni, jurisprudence is Yemeni, and wisdom is Yemeni."