(the mother of the faithful believers) I never saw Messenger of Allah ﷺ offering the night prayer while sitting except in his old age and then he used to recite while sitting and whenever he wanted to bow he would get up and recite thirty or forty verses (while standing) and then bow.  

عَنْ عَائِشَةَ ؓ أُمِّ الْمُؤْمِنِينَ أَنَّهَا أَخْبَرَتْهُ أَنَّهَا لَمْ تَرَ رَسُولَ اللَّهِ ﷺ يُصَلِّي صَلاَةَ اللَّيْلِ قَاعِدًا قَطُّ حَتَّى أَسَنَّ فَكَانَ يَقْرَأُ قَاعِدًا حَتَّى إِذَا أَرَادَ أَنْ يَرْكَعَ قَامَ فَقَرَأَ نَحْوًا مِنْ ثَلاَثِينَ آيَةً أَوْ أَرْبَعِينَ آيَةً ثُمَّ رَكَعَ  

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet ﷺ told him that she had never seen the Messenger of Allah ﷺ doing night prayers sitting down until he was getting on in years. He would recite sitting down until when he wanted to go into ruku, he would stand up and recite about thirty or forty ayats and then go into ruku.  

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّهَا أَخْبَرَتْهُ أَنَّهَا لَمْ تَرَ رَسُولَ اللَّهِ ﷺ يُصَلِّي صَلاَةَ اللَّيْلِ قَاعِدًا قَطُّ حَتَّى أَسَنَّ فَكَانَ يَقْرَأُ قَاعِدًا حَتَّى إِذَا أَرَادَ أَنْ يَرْكَعَ قَامَ فَقَرَأَ نَحْوًا مِنْ ثَلاَثِينَ أَوْ أَرْبَعِينَ آيَةً ثُمَّ رَكَعَ  

[Machine] The Messenger of Allah ﷺ did not used to pray the night prayer sitting until he became old. He used to recite while sitting, and when he wanted to bow, he stood up and recited about thirty or forty verses, then he bowed.  

لَمْ تَرَ رَسُولَ اللهِ ﷺ يُصَلِّي صَلَاةَ اللَّيْلِ قَاعِدًا قَطُّ حَتَّى أَسَنَّ فَكَانَ يَقْرَأُ قَاعِدًا حَتَّى إِذَا أَرَادَ أَنْ يَرْكَعَ قَامَ فَقَرَأَ نَحْوًا مِنْ ثَلَاثِينَ أَوْ أَرْبَعِينَ آيَةً ثُمَّ رَكَعَ