It was narrated from Abu Salamah, that Umm Salamah said: "By the One in Whose Hand is my soul. The Messenger of Allah (ﷺ) did not pass away until most of his prayers were offered sitting down, except for the obligatory prayers, and the dearest of actions to him were those which were done persistently, even if they were few."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عَبْدُ اللَّهِ بْنُ عَبْدِ الصَّمَدِ، قَالَ حَدَّثَنَا يَزِيدُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي سَلَمَةَ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ وَالَّذِي نَفْسِي بِيَدِهِ مَا مَاتَ رَسُولُ اللَّهِ صلى الله عليه وسلم حَتَّى كَانَ أَكْثَرُ صَلاَتِهِ قَاعِدًا إِلاَّ الْمَكْتُوبَةَ وَكَانَ أَحَبُّ الْعَمَلِ إِلَيْهِ مَا دَاوَمَ عَلَيْهِ وَإِنْ قَلَّ . خَالَفَهُ عُثْمَانُ بْنُ أَبِي سُلَيْمَانَ فَرَوَاهُ عَنْ أَبِي سَلَمَةَ عَنْ عَائِشَةَ .
sunnah.com