Sunan an-Nasa'i, Volume 2, Book 20, Hadith 1655 (DarusSalam) ⓘ

It was narrated from Abu Salamah, that Umm Salamah said: "The Messenger of Allah 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."

أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، حَدَّثَنَا خَالِدٌ، عَنْ شُعْبَةَ، عَنْ أَبِي إِسْحَاقَ، قَالَ سَمِعْتُ أَبَا سَلَمَةَ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ مَا مَاتَ رَسُولُ اللَّهِ صلى الله عليه وسلم حَتَّى كَانَ أَكْثَرُ صَلاَتِهِ قَاعِدًا إِلاَّ الْفَرِيضَةَ وَكَانَ أَحَبُّ الْعَمَلِ إِلَيْهِ أَدْوَمَهُ وَإِنْ قَلَّ ‏.‏