Sahih Bukhari Volume 2, Book 25, Hadith 1663

وَقَالَ اللَّيْثُ حَدَّثَنِي عُقَيْلٌ، عَنِ ابْنِ شِهَابٍ، قَالَ أَخْبَرَنِي سَالِمٌ، أَنَّ الْحَجَّاجَ بْنَ يُوسُفَ، عَامَ نَزَلَ بِابْنِ الزُّبَيْرِ ـ رضى الله عنهما ـ سَأَلَ عَبْدَ اللَّهِ ـ رضى الله عنه ـ كَيْفَ تَصْنَعُ فِي الْمَوْقِفِ يَوْمَ عَرَفَةَ فَقَالَ سَالِمٌ إِنْ كُنْتَ تُرِيدُ السُّنَّةَ فَهَجِّرْ بِالصَّلاَةِ يَوْمَ عَرَفَةَ‏.‏ فَقَالَ عَبْدُ اللَّهِ بْنُ عُمَرَ صَدَقَ‏.‏ إِنَّهُمْ كَانُوا يَجْمَعُونَ بَيْنَ الظُّهْرِ وَالْعَصْرِ فِي السُّنَّةِ‏.‏ فَقُلْتُ لِسَالِمٍ أَفَعَلَ ذَلِكَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَقَالَ سَالِمٌ وَهَلْ تَتَّبِعُونَ فِي ذَلِكَ إِلاَّ سُنَّتَهُ

Ibn Shihab said: Salim said,"In the year when Al-Hajjaj bin Yusuf attacked Ibn Az-Zubair (R.A.), the former asked Abdullah(Ibn Umar) What to do during the stay on the day of Arafa(9th of Dhul Hajjah).I said to him,"If you want to follow the sunnah(the legal way of the prophet(s.a.w.)you should offer the Salat just after midday on the day of Arafa.Abdullah bin Umar said,He(Salim) has spoken the truth."They(the Companions of the Prophet(s.a.w.)used to offer the Zuhr and the Asr prayer together according to the sunnah,I asked Salim,"Did Allah's Messenger do that?"Salim said," And in doing that do you(people)follow anything else except his Sunnah?