Missing Arafah entirely invalidates the Haji — the jamaah haji must exit Ihram via Umrah rites, sacrifice a sheep, and repeat Haji the following year, as 'Haji is Arafah.'
Standing at Arafah (Wuquf al-Arafah) is the most critical pillar (rukun) of Haji. Nabi Muhammad (shallallahu alaihi wa sallam) declared: 'Haji is Arafah' — meaning that without this rite, there is no Haji. This is the one ritual for which there is no substitute, compensation, or workaround. All four schools of jurisprudence agree on this point unanimously.
The time for standing at Arafah extends from after the sun passes its zenith (zawal) on the 9th of Dzulhijjah until the dawn (Fajr) of the 10th of Dzulhijjah. A jamaah haji only needs to be present within the boundaries of Arafah for even a brief moment during this window — even standing for a few minutes at night counts. However, the Sunnah is to be present from after Dhuhr until sunset.
If a jamaah haji completely misses this window — due to illness, being lost, transport failure, or any other reason — their Haji is invalid. They must then exit the state of Ihram by performing the rites of Umrah (Tawaf and sa'i, followed by cutting the hair), and they are obligated to perform Haji the following year. They must also offer a sacrifice (a sheep). This underscores why proper planning, early arrival at Arafah, and knowing the boundaries are absolutely essential.
Nabi (shallallahu alaihi wa sallam) said: 'Haji is Arafah. Whoever arrives at Arafah on the night of Jam' (Muzdalifah) before Fajr has caught the Haji.'
Nabi (shallallahu alaihi wa sallam) said: 'Haji is Arafah. Whoever arrives at Arafah on the night of Jam' (Muzdalifah) before Fajr has caught the Haji.'
Source: Ibn Qudamah, Al-Mughni; al-Nawawi, Al-Majmu
Nabi (shallallahu alaihi wa sallam) said: 'Haji is Arafah. Whoever arrives at Arafah on the night of Jam' (Muzdalifah) before Fajr has caught the Haji.'
Sunan al-Tirmidhi #889 (sahih)