It is recommended to touch the two Yemeni Corners in Tawaf and not the other two corners
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَابْنُ، نُمَيْرٍ جَمِيعًا عَنْ أَبِي خَالِدٍ، - قَالَ أَبُو بَكْرٍ حَدَّثَنَا أَبُو خَالِدٍ الأَحْمَرُ، - عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، قَالَ رَأَيْتُ ابْنَ عُمَرَ يَسْتَلِمُ الْحَجَرَ بِيَدِهِ ثُمَّ قَبَّلَ يَدَهُ وَقَالَ مَا تَرَكْتُهُ مُنْذُ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَفْعَلُهُ .
NAfi' (Allah be pleased with him) reported: I saw'lbn 'Umar (Allah be pleased with them) touching the Stone with his hand and then kissing his hand. and he said: I have never abandoned it since I saw Allah's Messenger (way peace be upon him) doing It.