Sahih al-Bukhari 252

Abū Jaʿfar narrated that he and his father were with Jābir ibn ʿAbd Allāh, and some other people were also present. They asked him about bathing. He said: ‘One ṣāʿ [of water] should suffice for you.’ One man said: ‘It is not sufficient for me.’ Jābir replied: ‘It was sufficient for one who had more hair than you and was superior to you.’ Then he led us in Prayer wearing a thawb.

Translation: Ahmadiyya Muslim Jamaat

Book 3: Taking a bath with a Sa' of water or so (One Sa' = 3 kilograms approx.)