Musnad Ahmad 98:1

Yahya ibn Sa'id narrated to us, from Muhammad ibn 'Amr, who said: 'Ubaydah ibn Sufyan al-Hadrami narrated to me, from Abu al-Ja'd al-Damri—and he had companionship [with the Prophet]—who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever leaves three Jumu'ah [prayers] out of negligence, without an excuse, Allah will place a seal upon his heart."