Musnad Ahmad 32:1394

Abu al-Mughirah narrated to us, he said: al-Awza'i narrated to us, Qatadah narrated to me, from Anas ibn Malik and Abu Sa'id al-Khudri—and Abu al-Mughirah narrated it to us from Anas, from Abu Sa'id, then he retracted—that the Prophet, peace and blessings of Allah be upon him, said: "There will be disagreement and division in my Ummah; a people who speak well but act poorly. They recite the Quran, but it does not pass beyond their collarbones. One of you would belittle his own prayer compared to their prayer, and his own fasting compared to their fasting. They pass through the religion just as an arrow passes through the game, then they do not return until the arrow returns to its notch. They are the worst of creation and creatures. Blessed is he who kills them and whom they kill. They call to the Book of Allah, while they have nothing of it. Whoever fights them is closer to Allah than they are." They said: "O Messenger of Allah, what is their sign?" He said: "Shaving [the head]."