Musnad Ahmad 30:1732

Sulayman narrated to us, Isma'il informed us, al-'Ala' informed me, from his father, from Abu Hurayrah, that the Prophet, peace and blessings of Allah be upon him, said: "Beware of the two cursers." They said: "And what are the two cursers, O Messenger of Allah?" He said: "The one who relieves himself in the path of the people or in their shade."