Musnad Ahmad 31:99

Isma'il narrated to us, from Hisham al-Dastawa'i, he said: Yahya ibn Abi Kathir narrated to us, from Abu Rif'ah, from Abu Sa'id al-Khudri, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The Suhur is a blessed meal, so do not leave it, even if one of you takes a gulp of water, for Allah the Almighty and His angels send blessings upon those who eat the Suhur."