Sunan Ibn Majah, Chapter: The Chapters on Hajj

"On the morning of Aqabah, when he was atop his she-camel, the Messenger of Allah (saw) said: 'Pick up some pebbles for me.' So I picked up seven pebbles for him, suitable for Khadhf.* He began to toss them in his hand, saying: 'Throw something like these.' Then he said: 'O people, beware of exaggeration in religious matters for those who came before you were doomed because of exaggeration in religious matters.'"