Sunan Ibn Majah Book 37, Hadith 4237

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 أَحَبَّ الأَعْمَالِ إِلَيْهِ، الْعَمَلُ الصَّالِحُ الَّذِي يَدُومُ عَلَيْهِ الْعَبْدُ وَإِنْ كَانَ يَسِيرًا ‏.‏

It was narrated that Umm Salamah said:“By the One Who took his (ﷺ) soul, he did not die until most of his prayers were offered sitting down. And the most beloved of deeds to him was a righteous deed which a person persists in doing, even if it is something small.”