Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that on the day of Arafah, while al-Fadl bin Abbas (may Allah be pleased with him) was riding behind the Messenger of Allah (peace and blessings be upon him), Sayyiduna al-Abbas (may Allah be pleased with him) said: When the people said the Takbir, I said (to myself): Al-Fadl will tell me what the Messenger of Allah (peace and blessings be upon him) did. (Sayyiduna al-Fadl, may Allah be pleased with him) said: When the Messenger of Allah (peace and blessings be upon him) set off on the evening of Arafah, the people set off with him. The Messenger of Allah (peace and blessings be upon him) kept pulling the nose-rein of his camel to hold it back, and kept calling out: "O people! Adopt calm and tranquillity." Until, when he reached the valley of Muhassir, he went somewhat faster, and began saying: "You must use small pebbles."
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15781