Jumu'a
Malik :: Book 5 : Hadith 5.9.22
Yahya related to me from Malik that Safwan ibn Sulaym said, "If anyone omits jumua three times without reason or illness, Allah will set a seal on his heart." (Malik said, "I don't know if it was from the Messenger of Allah, may Allah bless him and grant him peace, or not.")