Musnad Ahmad 25:1240

'Abd al-Samad narrated to us, Hisham al-Dastawa'i narrated to us, from Yahya, who said: Abu Salam narrated from al-Hakam ibn Mina', that he heard 'Abdullah ibn 'Umar and 'Abdullah ibn 'Abbas, that they both heard the Messenger of Allah, peace and blessings of Allah be upon him, saying upon the planks of his pulpit: "People must cease neglecting the Friday prayers, or Allah will surely seal their hearts, and then they will surely be written among the heedless."