Musnad Abu Ya'la al-Mawsili 154:112

Zuhayr narrated to us, Yazid bin Harun narrated to us, Hisham al-Dastawa'i informed us, from Yahya bin Abi Kathir, from Abu Salam, from al-Hakam bin Mina, from Ibn Umar and Ibn Abbas, that they both testified regarding the Messenger of Allah (may Allah bless him and grant him peace) that he said while he was on the pulpit: "People must cease abandoning the Friday prayers, or Allah will surely seal their hearts, and they will surely be among the heedless."