Musannaf Ibn Abi Shayba 17:1049

Abu Mu'awiyah narrated to us, from 'Asim, from 'Awn ibn 'Abdullah, from Abu Hurayrah, who said: "Beware of the causes of cursing." They said, "And what are the causes of cursing?" He said, "The thoroughfare of sitting on the road and under a tree in which the rider seeks shade."