Authentic
Sunan Ibn Majah 270
"The Messenger of Allah said: 'A Mudd is sufficient for the ablution and a Sa' is sufficient for the bath.' A man said: 'It is not sufficient for us.'" He (the narrator) said: "It was sufficient for one who is better than you and had more hair" meaning the Prophet.
" يُجْزِئُ مِنَ الْوُضُوءِ مُدٌّ وَمِنَ الْغُسْلِ صَاعٌ " . فَقَالَ رَجُلٌ لاَ يُجْزِئُنَا . فَقَالَ قَدْ كَانَ يُجْزِئُ مَنْ هُوَ خَيْرٌ مِنْكَ وَأَكْثَرُ شَعَرًا . يَعْنِي