Sunan an-Nasa'i, Volume 1, Book 6, Hadith 511 (DarusSalam)

It was narrated that Abu Salamah said: "We prayed at the time of 'Umar bin 'Abdul-'Aziz, then we went to Anas bin Malik and found him praying. when he finished he said to us: 'Have you prayed?' We said: 'We prayed Zuhr.' He said: 'I prayed 'Asr.' They said: 'You have prayed early.' He said: 'Rather I prayed as I saw my companions pray.'"

أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا أَبُو عَلْقَمَةَ الْمَدَنِيُّ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ عَمْرٍو، عَنْ أَبِي سَلَمَةَ، قَالَ صَلَّيْنَا فِي زَمَانِ عُمَرَ بْنِ عَبْدِ الْعَزِيزِ ثُمَّ انْصَرَفْنَا إِلَى أَنَسِ بْنِ مَالِكٍ فَوَجَدْنَاهُ يُصَلِّي فَلَمَّا انْصَرَفَ قَالَ لَنَا أَصَلَّيْتُمْ قُلْنَا صَلَّيْنَا الظُّهْرَ ‏.‏ قَالَ إِنِّي صَلَّيْتُ الْعَصْرَ ‏.‏ فَقَالُوا لَهُ عَجَّلْتَ ‏.‏ فَقَالَ إِنَّمَا أُصَلِّي كَمَا رَأَيْتُ أَصْحَابِي يُصَلُّونَ ‏.‏

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also referenced under: Book 6, Hadith 514 (In-Book)