Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) said: "At the beginning of Islam, the saying of the Ansar was: 'Water (the ritual bath) is due only from water (emission).' Then after that the command of ghusl (ritual bath) came (for intercourse even without emission)."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5675