Yahya related to me from Malik that Safwan ibn Sulaym said, "Ifanyone omits jumua three times without reason or illness, Allah willset a seal on his heart." (Malik said, "I don't know if it was fromthe Messenger of Allah, may Allah bless him and grant him peace, ornot.") (AR)
USC-MSA web (English) reference: Book 5, Hadith 22 (AR)
Arabic reference (AR): Book 5, Hadith 245 (AR)