It is recommended to kiss the black stone during circumambulation (Tawaf)
وَحَدَّثَنِي حَرْمَلَةُ بْنُ يَحْيَى، أَخْبَرَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي يُونُسُ، وَعَمْرٌو، ح وَحَدَّثَنِي هَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ، حَدَّثَنِي ابْنُ وَهْبٍ، أَخْبَرَنِي عَمْرٌو، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمٍ، أَنَّحَدَّثَهُ قَالَ قَبَّلَ عُمَرُ بْنُ الْخَطَّابِ الْحَجَرَ ثُمَّ قَالَ أَمَ وَاللَّهِ لَقَدْ عَلِمْتُ أَنَّكَ حَجَرٌ وَلَوْلاَ أَنِّي رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُقَبِّلُكَ مَا قَبَّلْتُكَ . زَادَ هَارُونُ فِي رِوَايَتِهِ قَالَ عَمْرٌو وَحَدَّثَنِي بِمِثْلِهَا زَيْدُ بْنُ أَسْلَمَ عَنْ أَبِيهِ أَسْلَمَ .
Salim narrated on the authority of his father (Allah be pleased with him) that 'Umar b. al-Khattib (Allah be pleased with him) kissed (the Black Stone) and then said: By Allah, I know that you are a stone and if I were not to see Allah's Messenger (ﷺ) kissing you, I would not have kissed you. Harun said in his narration: A hadith like this has been transmitted to me by Zaid b. Aslam on the authority of his father Aslam.