Is it permissible to combine and shorten the Dhuhr and Asr prayers on the day of Arafah at home before going to Arafah, and is it necessary to repeat those prayers?

It is Sunnah (definition) for the pilgrim to combine Dhuhr and Asr prayers at Arafat with jum' taqdeem (combining and performing earlier). If someone prays them outside Arafat, their prayer is valid, but they have deviated from the Sunnah. Shortening the prayer without travel or a ritual (like Hajj) is invalid, and it must be re-prayed. Combining prayers without travel is permissible if there is a need. If you are outside Arafat and there is no crowding, you are not permitted to combine prayers, and the second prayer becomes invalid. Scholars have unanimously agreed on the permissibility of combining prayers at Arafat for anyone who prays with the Imam, including the people of Makkah, but the people of Makkah are not allowed to shorten the prayer. It is Sunnah to enter into ihram (definition) for Hajj on the eighth day and to spend the night in Mina. However, if you enter into ihram on the ninth day, your ihram is still valid.