Sunan an-Nasa'i, Volume 3, Book 22, Hadith 2349 (DarusSalam) ⓘ
It was narrated that 'Aishah said: "The Messenger of Allah used to fast until we said: 'He does not want to break his fast.' And he used not to fast until we said: 'He does not want to fast."'
أَخْبَرَنَا مُحَمَّدُ بْنُ النَّضْرِ بْنِ مُسَاوِرٍ الْمَرْوَزِيُّ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ مَرْوَانَ أَبِي لُبَابَةَ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصُومُ حَتَّى نَقُولَ مَا يُرِيدُ أَنْ يُفْطِرَ وَيُفْطِرُ حَتَّى نَقُولَ مَا يُرِيدُ أَنْ يَصُومَ .
also referenced under: Hadith 2347 (Reference) & Book 22, Hadith 258 (In-Book)