This is based on the statement of Ibn ‘Umar in which he said “I never saw the Prophet (peace be upon him) touching any other parts of Ka’bah except the two corners: The Black Stone and the Yemeni corner.” And he added, “No matter how hard and difficult the circumstances, I have not failed to touch these two corners – the Yemeni Corner and the Black Stone – ever since I saw the Prophet (peace be upon him) doing so.” (Reported by Bukhari and Muslim)
A pilgrim making tawaf touches these two corners, and no others, because of their special merits and excellence. The Black Stone is distinguished by two things:
1. it is placed on the foundations raised by the Prophet Ibrahim (peace be upon him), and
2. it marks the beginning as well as the end of tawaf. The Yemeni corner is directly opposite to it and, like the Black Stone, it is also laid on the foundations raised by Ibrahim.
When Ibn ‘Umar was told about ‘Aishah’s statement that “Some of the Hijr Isma’il is part of the Ka’bah” he said: “I think that ‘Aishah heard that from the Prophet (peace be upon him). I think that the Prophet (peace be upon him) never failed to touch them while making a tawaf These two, however, are not at the foundations of the House, and the people circumambulate around the Hijr because of that. (Abu Dawud)
The Muslim community, however, is in agreement concerning the desirability of touching these two Yemeni corners. A person making tawaf of Ka’bah may not touch the other two corners. Ibn Hibban has reported in his Sahih that the Prophet (peace be upon him) said: “The Black Stone and the Yemeni corner cause the sins to be forgiven.”