Sahih al-Bukhari 548
Sahih al-Bukhari · Book 9: Times of the Prayers · The time of the Asr prayer
Narrated Anas bin Malik:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ ، عَنْ مَالِكٍ ، عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ أَبِي طَلْحَةَ ، عَنْ أَنَسِ بْنِ مَالِكٍ ، قَالَ كُنَّا نُصَلِّي الْعَصْرَ ثُمَّ يَخْرُجُ الإِنْسَانُ إِلَى بَنِي عَمْرِو بْنِ عَوْفٍ فَنَجِدُهُمْ يُصَلُّونَ الْعَصْرَ.
We used to pray the `Asr prayer and after that if someone happened to go to the tribe of Bani `Amr bin `Auf, he would find them still praying the `Asr (prayer).