Musnad Ahmad 30:904

'Abd al-Rahman narrated to us, from Sufyan, from 'Asim, from 'Ubayd, the freed slave of Abu Ruhm, from Abu Hurayrah, who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Many an oath does not ascend to Allah in this spot." He said: And I saw the slave traders in it afterwards.