Musnad Abu Ya'la al-Mawsili 159:118

Ishaq ibn Abi Isra'il narrated to us, Waki' narrated to us, from Ibn Abi Layla, from 'Ata', from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Eat the pre-dawn meal (suhur), for indeed there is blessing in the pre-dawn meal."