Musnad Ahmad 25:1389

Yahya and Isma'il—the meaning being the same—said: 'Awf narrated to us, Ziyad ibn Husayn narrated to me, from Abu al-'Aliyah al-Riyahi, from Ibn 'Abbas—Yahya said: 'Awf did not know if it was 'Abdullah or al-Fadl—he said: The Messenger of Allah (peace and blessings of Allah be upon him) said to me on the morning of al-'Aqabah, while he was standing on his mount: "Come, pick up for me." So I picked up for him pebbles, which were the pebbles of al-khadhf (throwing with the thumb and index finger). He placed them in his hand and said: "With the likes of these," twice. He gestured with his hand—and Yahya indicated that he raised it—and said: "Beware of extremism, for those who were before you were only destroyed by extremism in religion."