Sahih Bukhari

Narrated Salim bin `Abdullah bin `Umar:`Abdul-Malik bin Marwan wrote to Al-Hajjaj that he should follow `Abdullah bin `Umar in all the ceremonies of Hajj. So when it was the Day of `Arafat (9th of Dhul-Hijja), and after the sun had deviated or had declined from the middle of the sky, I and Ibn `Umar came and he shouted near the cotton (cloth) tent of Al-Hajjaj, ""Where is he?"" Al-Hajjaj came out. Ibn `Umar said, ""Let us proceed (to `Arafat)."" Al-Hajjaj asked, ""Just now?"" Ibn `Umar replied, ""Yes."" Al-Hajjaj said, ""Wait for me till I pour water on me (i.e. take a bath)."" So, Ibn `Umar dismounted (and waited) till Al-Hajjaj came out. He was walking between me and my father. I informed Al-Hajjaj, ""If you want to follow the Sunna today, then you should shorten the sermon and then hurry up for the stay (at `Arafat)."" Ibn `Umar said, ""He (Salim) has spoken the truth