Sunan an-Nasa'i, Book 20, Hadith 55 (In-Book) ⓘ

It was narrated that Aishah said: "The Messenger of Allah did not refrain from (kissing) my forehead when he was fasting, and he did not die until most of his prayers were offered sitting down." Then she said something to the effect that (referred to the prayers) other than the obligatory prayers. "And the dearest of actions to him was that in which a person persists, even if it is little."

أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، عَنْ حَدِيثِ أَبِي عَاصِمٍ، قَالَ حَدَّثَنَا عُمَرُ بْنُ أَبِي زَائِدَةَ، قَالَ حَدَّثَنِي أَبُو إِسْحَاقَ، عَنِ الأَسْوَدِ، عَنْ عَائِشَةَ، قَالَتْ مَا كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَمْتَنِعُ مِنْ وَجْهِي وَهُوَ صَائِمٌ وَمَا مَاتَ حَتَّى كَانَ أَكْثَرُ صَلاَتِهِ قَاعِدًا ثُمَّ ذَكَرَتْ كَلِمَةً مَعْنَاهَا إِلاَّ الْمَكْتُوبَةَ وَكَانَ أَحَبُّ الْعَمَلِ إِلَيْهِ مَا دَامَ عَلَيْهِ الإِنْسَانُ وَإِنْ كَانَ يَسِيرًا ‏.‏ خَالَفَهُ يُونُسُ رَوَاهُ عَنْ أَبِي إِسْحَاقَ عَنِ الأَسْوَدِ عَنْ أُمِّ سَلَمَةَ ‏.‏