Musnad Ahmad 30:3096

Waki’ narrated to us, from al-A’mash, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There are three whom Allah will not speak to on the Day of Resurrection, nor will He look at them, nor will He purify them, and they shall have a painful punishment: a man who withheld from a wayfarer the surplus of water he had; a man who swore an oath regarding merchandise after the afternoon prayer—meaning falsely; and a man who pledged allegiance to an Imam; if he gave him [what he wanted], he fulfilled it for him, and if he did not give him, he did not fulfill it for him."