Sayyidah Hafsah (may Allah be pleased with her) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Jumu'ah is obligatory on every adult, and ghusl (ritual bath) is obligatory on whoever comes to Jumu'ah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5577