Sahih Muslim Book - 5, Hadith - 1427

وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِىُّ قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ زَيْدِ بْنِ أَسْلَمَ عَنِ الْقَعْقَاعِ بْنِ حَكِيمٍ عَنْ أَبِى يُونُسَ مَوْلَى عَائِشَةَ أَنَّهُ قَالَ أَمَرَتْنِى عَائِشَةُ أَنْ أَكْتُبَ لَهَا مُصْحَفًا وَقَالَتْ إِذَا بَلَغْتَ هَذِهِ الآيَةَ فَآذِنِّى (حَافِظُوا عَلَى الصَّلَوَاتِ وَالصَّلاَةِ الْوُسْطَى) فَلَمَّا بَلَغْتُهَا آذَنْتُهَا فَأَمْلَتْ عَلَىَّ حَافِظُوا عَلَى الصَّلَوَاتِ وَالصَّلاَةِ الْوُسْطَى وَصَلاَةِ الْعَصْرِ. وَقُومُوا لِلَّهِ قَانِتِينَ. قَالَتْ عَائِشَةُ سَمِعْتُهَا مِنْ رَسُولِ اللَّهِ -صلى الله عليه وسلم-.

It was narrated that Abu Yunus, the freed slave of 'Aishah, said: "'Aishah told me to write a Mushaf for her, and she said: 'When you reach this verse - Guard strictly (five obligatory) As-Salawat (the prayers) especially the middle Salat... - call me.' When I reached it, I called her, and she dictated to me the words of Allah: 'Guard strictly (five obligatory) As-Salawat (the prayers) especially the middle Salat and 'Asr prayer. And stand before Allah with obedience.' 'Aishah said: 'I heard it from the Messenger of Allah (s.a.w)."'