Sahih Bukhari Volume 1, Book 9, Hadith 549

حَدَّثَنَا ابْنُ مُقَاتِلٍ، قَالَ أَخْبَرَنَا عَبْدُ اللَّهِ، قَالَ أَخْبَرَنَا أَبُو بَكْرِ بْنُ عُثْمَانَ بْنِ سَهْلِ بْنِ حُنَيْفٍ، قَالَ سَمِعْتُ أَبَا أُمَامَةَ، يَقُولُ صَلَّيْنَا مَعَ عُمَرَ بْنِ عَبْدِ الْعَزِيزِ الظُّهْرَ، ثُمَّ خَرَجْنَا حَتَّى دَخَلْنَا عَلَى أَنَسِ بْنِ مَالِكٍ فَوَجَدْنَاهُ يُصَلِّي الْعَصْرَ فَقُلْتُ يَا عَمِّ، مَا هَذِهِ الصَّلاَةُ الَّتِي صَلَّيْتَ قَالَ الْعَصْرُ، وَهَذِهِ صَلاَةُ رَسُولِ اللَّهِ صلى الله عليه وسلم الَّتِي كُنَّا نُصَلِّي مَعَهُ

Narrated By Abu Bakr bin Uthman bin Sahl bin Hunaif : That he heard Abu Umama saying: We prayed the Zuhr prayer with 'Umar bin Abdul Aziz and then went to Anas bin Malik and found him offering the Asr prayer. I asked him, "O uncle! Which prayer have you offered?" He said 'The Asr and this is (the time of) the prayer of Allah s Apostle which we used to pray with him."