Musnad Ahmad 27:1172

'Abd al-Razzaq narrated to us, Ma'mar and al-Thawri narrated to us, from 'Ata' ibn al-Sa'ib, from 'Abd Allah ibn 'Ubayd ibn 'Umayr, from his father, from Ibn 'Umar, that the Prophet (peace and blessings of Allah be upon him) said: "Verily, wiping the Yemeni Corner and the Black Corner sheds sins, a shedding."