The Messenger of Allah ﷺ said, "Whoever reaches Arafat and stands there, and reaches Muzdalifa, has completed his Hajj. Whoever misses Arafat has missed the Hajj, so let him exit ihram with an Umra, and he must perform the Hajj the following year."
قال رسول الله ﷺ: من أدرك عرفات فوقف بها والمزدلفة فقد تم حجه، ومن فاته عرفات فقد فاته الحج فليحل بعمرة وعليه الحج من قابل.
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Daraqutni (2519) narrated it through Ibn Abu Layla, from Ataa, from Ibn Abbas, who said, then he mentioned it. Ibn Abu Layla has weak memory, but he was not alone in narrating it, for Bayhaqi (5/174) narrated it through Abdullah bin Habib bin Abu Thabit, from Ataa, in a similar manner, except that he did not mention Muzdalifa. No attention should be paid to the corroboration of Umar bin Qays from Ataa, for he is discarded as a narrator, and Tabarani narrated it through his route in al-Kabir (11/202).