Musnad Ahmad 31:761

'Ali ibn 'Abdullah narrated to us, Hushaym narrated to us, he said: Mujalid informed us, from Abu al-Wadak, from Abu Sa'id al-Khudri, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Three [types of people] Allah laughs at: A man who stands [in prayer] at night, a group when they stand in rows for prayer, and a group when they stand in rows for fighting."