صَحِيحُ مُسْلِمٍ
Sahih Muslim 730 b
The Book of Prayer - Travellers
It is permissible to offer voluntary prayers standing or sitting, and to stand and sit in the same rak`ah
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا حَمَّادٌ، عَنْ بُدَيْلٍ، وَأَيُّوبَ، عَنْ عَبْدِ اللَّهِ بْنِ شَقِيقٍ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي لَيْلاً طَوِيلاً فَإِذَا صَلَّى قَائِمًا رَكَعَ قَائِمًا وَإِذَا صَلَّى قَاعِدًا رَكَعَ قَاعِدًا .
'A'isha reported that the Messenger of Allah (ﷺ) would pray in the night for a long time, and when he prayed standing be bowed in a standing posture, and when he prayed sitting, he bowed in a sitting posture.
Sahih Muslim, 730 bSahihصحيح