Musnad Ahmad 1007:42

Abu Sa’id narrated to us, ‘Abd al-‘Aziz ibn Muhammad narrated to us, from Usayd, from ‘Abd Allah ibn Abi Qatadah, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever leaves the Friday [prayer] three times without necessity, a seal is placed upon his heart."