Sunan Ibn Majah Book 5, Hadith 1225

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي سَلَمَةَ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ وَالَّذِي ذَهَبَ بِنَفْسِهِ ـ صلى الله عليه وسلم ـ مَا مَاتَ حَتَّى كَانَ أَكْثَرُ صَلاَتِهِ وَهُوَ جَالِسٌ وَكَانَ أَحَبُّ الأَعْمَالِ إِلَيْهِ الْعَمَلَ الصَّالِحَ الَّذِي يَدُومُ عَلَيْهِ الْعَبْدُ وَإِنْ كَانَ يَسِيرًا ‏.‏

It was narrated that Umm Salamah said:‘By the One Who took his soul (i.e., the soul of the Prophet (ﷺ)), he did not die until he offered most of his prayers sitting down. And the dearest of the actions to him was the righteous action that the person does regularly, even if it were a little.”