Abdullah bin Umar and Abu Hurayrah (may Allah be pleased with them both) both heard the Messenger of Allah (peace and blessings be upon him) say: "People must stop abandoning Jumu'ah, or else Allah will seal their hearts, and then they will be among the heedless."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5571