In al-Mu'jam al-Awsat, on the authority of Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both),
this report is recorded: the Prophet (peace and blessings be upon him) said: "One mudd (of water) suffices for ablution, and one sa' (of water) for the ritual bath." Its chain contains a narrator, Abd al-Aziz bin Abd al-Rahman al-Balisi, on whose weakness the hadith scholars are agreed.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1100