AR-RUKNU ‘L-YAMANI الركن اليماني
The Yamani pillar. The south corner of the Ka’bah, said to be one of the most ancient parts of the temple. [MASJIDU ‘L-HARAM.]
Burkhardt says: “In the south-east corner of the Ka’bah, or as the Arabs call it, Rokn of Yamany, there is another stone about five feet from the ground; it is one foot and a half in length, and two inches in breadth, placed upright, and of the common Meccah stone. This the people walking round the Ka’bah touch only with the right hand; they do not kiss it.” (Captain Burton says he had frequently seen it kissed by men and women.)
Burton remarks: “The Rukn el Yamani is a corner facing the south. The part alluded to (by Burkhardt) is the wall of the Ka’bah, between the Shami and Yemani angles, distant about three feet from the latter, and near the site of the old western door, long since closed. The stone is darker and redder then the rest of the wall, it is called El Mustajab – (or Mustajab min el Zunub, or Mustajab el Dua, “where prayer is granted”). Pilgrims here extend their arms, press their bodies against the building, and beg pardon for their sins.” (El Medinah and Mecca. vol. ii. p. 160.)

Based on Hughes, Dictionary of Islam