It is recommended to kiss the black stone during circumambulation (Tawaf)
وَحَدَّثَنَا مُحَمَّدُ بْنُ أَبِي بَكْرٍ الْمُقَدَّمِيُّ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ أَيُّوبَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ عُمَرَ، قَبَّلَ الْحَجَرَ وَقَالَ إِنِّي لأُقَبِّلُكَ وَإِنِّي لأَعْلَمُ أَنَّكَ حَجَرٌ وَلَكِنِّي رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُقَبِّلُكَ .
Ibn 'Umar (Allah be pleased with them) reported that Umar (Allah be pleased with him) kissed the Stone and said: I am kissing you, whereas I know that you are a stone, but I saw Allah's Messenger (ﷺ) kissing you (that Is why I kiss you).