Sahih Muslim , Book 3, Hadith 61 (In-Book) ⓘ

Safina reported that Abu Bakr, the Companion of the Messenger of Allah (way peace be upon him), observed: The Messenger of Allah took a bath with one Sa' of water and performed ablution with one Mudd (of water) ; and in the hadith narrated by Ibn Hujr the words are: One Mudd sufficed for his (Holy Prophet's) ablution. And Ibn Hujr said that (his Shaikh) Isma'il was much advanced in age, and it was because of this that he could not fully rely on him for this tradition.

وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا ابْنُ عُلَيَّةَ، ح وَحَدَّثَنِي عَلِيُّ بْنُ حُجْرٍ، حَدَّثَنَا إِسْمَاعِيلُ، عَنْ أَبِي رَيْحَانَةَ، عَنْ سَفِينَةَ، - قَالَ أَبُو بَكْرٍ - صَاحِبُ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَغْتَسِلُ بِالصَّاعِ وَيَتَطَهَّرُ بِالْمُدِّ ‏.‏ وَفِي حَدِيثِ ابْنِ حُجْرٍ أَوْ قَالَ وَيُطَهِّرُهُ الْمُدُّ ‏.‏ وَقَالَ وَقَدْ كَانَ كَبِرَ وَمَا كُنْتُ أَثِقُ بِحَدِيثِهِ ‏.‏