It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The whole plain of Arafah is a place of standing (wuquf), and move up away from al-Sifah (the rocky slabs)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11521