Musnad Ahmad 30:1735

Sulayman narrated to us, Isma'il narrated to us, 'Amr—meaning Ibn Abi 'Amr—informed me, from Abu Sa'id al-Maqburi, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "How many a fasting person has no share of his fasting except hunger and thirst, and how many a person standing in prayer has no share of his standing except sleeplessness."