Sahih Bukhari Volume 4, Book 54, Number 417:
Narrated Muhammad bin Ibrahim bin Al-Harith:
from Abu Salama bin 'Abdur-Rahman who had a dispute with some people on a piece of land, and so he went to 'Aisha and told her about it. She said, "O Abu Salama, avoid the land, for Allah's Apostle said, 'Any person who takes even a span of land unjustly, his neck shall be encircled with it down seven earths.' "