Sahih Bukhari Volume 2, Book 26, Hadith Number 722.

Narated By Salim : ‘Abdul Malik wrote to Al-Hajjaj that he should not differ from Ibn ‘Umar during Hajj. On the Day of ‘Arafat, when the sun declined at midday, Ibn ‘Umar came along with me and shouted near Al-Hajjaj’s cotton (cloth) tent. Al-Hajjaj came Out, wrapping himself with a waist-sheet dyed with safflower, and said, “O Abu Abdur-Rahman! What is the matter?” He said, If you want to follow the Sunna (the tradition of the Prophet (p.b.u.h)) then proceed (to ‘Arafat).” Al-Hajjaj asked, “At this very hour?” Ibn ‘Umar said, “Yes.” He replied, “Please wait for me till I pour some water over my head (i.e. take a bath) and come out.” Then Ibn ‘Umar dismounted and waited till Al-Hajjaj came out. So, he (Al-Hajjaj) walked in between me and my father (Ibn ‘Umar). I said to him, “If you want to follow the Sunna then deliver a brief sermon and hurry up for the stay at ‘Arafat.” He started looking at ‘Abdullah (Ibn ‘Umar) (inquiringly), and when ‘Abdullah noticed that, he said that he had told the truth.