Musnad Ahmad 32:125

Ibn Abi ‘Adi narrated to us, from Sa‘id, and Ibn Ja‘far narrated to us, from Sa‘id, and al-Khaffaf, from Sa‘id, from Qatadah, from Anas, that the Prophet of Allah, peace and blessings of Allah be upon him, said: "What is the matter with people who raise their eyes toward the sky during their prayer?" And he spoke sternly regarding that, until he said: "They must cease from that, or their sight will surely be snatched away."